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basedocs.jl
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# This file is a part of Julia. License is MIT: https://julialang.org/license
module BaseDocs
@nospecialize # don't specialize on any arguments of the methods declared herein
struct Keyword
name::Symbol
end
macro kw_str(text)
return Keyword(Symbol(text))
end
"""
**Welcome to Julia $(string(VERSION)).** The full manual is available at
https://docs.julialang.org
as well as many great tutorials and learning resources:
https://julialang.org/learning/
For help on a specific function or macro, type `?` followed
by its name, e.g. `?cos`, or `?@time`, and press enter.
Type `;` to enter shell mode, `]` to enter package mode.
"""
kw"help", kw"Julia", kw"julia", kw""
"""
using
`using Foo` will load the module or package `Foo` and make its [`export`](@ref)ed names
available for direct use. Names can also be used via dot syntax (e.g. `Foo.foo` to access
the name `foo`), whether they are `export`ed or not.
See the [manual section about modules](@ref modules) for details.
"""
kw"using"
"""
import
`import Foo` will load the module or package `Foo`.
Names from the imported `Foo` module can be accessed with dot syntax
(e.g. `Foo.foo` to access the name `foo`).
See the [manual section about modules](@ref modules) for details.
"""
kw"import"
"""
export
`export` is used within modules to tell Julia which functions should be
made available to the user. For example: `export foo` makes the name
`foo` available when [`using`](@ref) the module.
See the [manual section about modules](@ref modules) for details.
"""
kw"export"
"""
abstract type
`abstract type` declares a type that cannot be instantiated, and serves only as a node in the
type graph, thereby describing sets of related concrete types: those concrete types
which are their descendants. Abstract types form the conceptual hierarchy which makes
Julia’s type system more than just a collection of object implementations. For example:
```julia
abstract type Number end
abstract type Real <: Number end
```
[`Number`](@ref) has no supertype, whereas [`Real`](@ref) is an abstract subtype of `Number`.
"""
kw"abstract type", kw"abstract"
"""
module
`module` declares a [`Module`](@ref), which is a separate global variable workspace. Within a
module, you can control which names from other modules are visible (via importing), and
specify which of your names are intended to be public (via exporting).
Modules allow you to create top-level definitions without worrying about name conflicts
when your code is used together with somebody else’s.
See the [manual section about modules](@ref modules) for more details.
# Examples
```julia
module Foo
import Base.show
export MyType, foo
struct MyType
x
end
bar(x) = 2x
foo(a::MyType) = bar(a.x) + 1
show(io::IO, a::MyType) = print(io, "MyType \$(a.x)")
end
```
"""
kw"module"
"""
__init__
`__init__()` function in your module would executes immediately *after* the module is loaded at
runtime for the first time (i.e., it is only called once and only after all statements in the
module have been executed). Because it is called *after* fully importing the module, `__init__`
functions of submodules will be executed *first*. Two typical uses of `__init__` are calling
runtime initialization functions of external C libraries and initializing global constants
that involve pointers returned by external libraries.
See the [manual section about modules](@ref modules) for more details.
# Examples
```julia
const foo_data_ptr = Ref{Ptr{Cvoid}}(0)
function __init__()
ccall((:foo_init, :libfoo), Cvoid, ())
foo_data_ptr[] = ccall((:foo_data, :libfoo), Ptr{Cvoid}, ())
nothing
end
```
"""
kw"__init__"
"""
baremodule
`baremodule` declares a module that does not contain `using Base` or local definitions of
[`eval`](@ref Base.eval) and [`include`](@ref Base.include). It does still import `Core`. In other words,
```julia
module Mod
...
end
```
is equivalent to
```julia
baremodule Mod
using Base
eval(x) = Core.eval(Mod, x)
include(p) = Base.include(Mod, p)
...
end
```
"""
kw"baremodule"
"""
primitive type
`primitive type` declares a concrete type whose data consists only of a series of bits. Classic
examples of primitive types are integers and floating-point values. Some example built-in
primitive type declarations:
```julia
primitive type Char 32 end
primitive type Bool <: Integer 8 end
```
The number after the name indicates how many bits of storage the type requires. Currently,
only sizes that are multiples of 8 bits are supported.
The [`Bool`](@ref) declaration shows how a primitive type can be optionally
declared to be a subtype of some supertype.
"""
kw"primitive type"
"""
macro
`macro` defines a method for inserting generated code into a program.
A macro maps a sequence of argument expressions to a returned expression, and the
resulting expression is substituted directly into the program at the point where
the macro is invoked.
Macros are a way to run generated code without calling [`eval`](@ref Base.eval), since the generated
code instead simply becomes part of the surrounding program.
Macro arguments may include expressions, literal values, and symbols. Macros can be defined for
variable number of arguments (varargs), but do not accept keyword arguments.
Every macro also implicitly gets passed the arguments `__source__`, which contains the line number
and file name the macro is called from, and `__module__`, which is the module the macro is expanded
in.
# Examples
```jldoctest
julia> macro sayhello(name)
return :( println("Hello, ", \$name, "!") )
end
@sayhello (macro with 1 method)
julia> @sayhello "Charlie"
Hello, Charlie!
julia> macro saylots(x...)
return :( println("Say: ", \$(x...)) )
end
@saylots (macro with 1 method)
julia> @saylots "hey " "there " "friend"
Say: hey there friend
```
"""
kw"macro"
"""
__module__
The argument `__module__` is only visible inside the macro, and it provides information
(in the form of a `Module` object) about the expansion context of the macro invocation.
See the manual section on [Macro invocation](@ref) for more information.
"""
kw"__module__"
"""
__source__
The argument `__source__` is only visible inside the macro, and it provides information
(in the form of a `LineNumberNode` object) about the parser location of the `@` sign from
the macro invocation. See the manual section on [Macro invocation](@ref) for more information.
"""
kw"__source__"
"""
local
`local` introduces a new local variable.
See the [manual section on variable scoping](@ref scope-of-variables) for more information.
# Examples
```jldoctest
julia> function foo(n)
x = 0
for i = 1:n
local x # introduce a loop-local x
x = i
end
x
end
foo (generic function with 1 method)
julia> foo(10)
0
```
"""
kw"local"
"""
global
`global x` makes `x` in the current scope and its inner scopes refer to the global
variable of that name.
See the [manual section on variable scoping](@ref scope-of-variables) for more information.
# Examples
```jldoctest
julia> z = 3
3
julia> function foo()
global z = 6 # use the z variable defined outside foo
end
foo (generic function with 1 method)
julia> foo()
6
julia> z
6
```
"""
kw"global"
"""
=
`=` is the assignment operator.
* For variable `a` and expression `b`, `a = b` makes `a` refer to the value of `b`.
* For functions `f(x)`, `f(x) = x` defines a new function constant `f`, or adds a new method to `f` if `f` is already defined; this usage is equivalent to `function f(x); x; end`.
* `a[i] = v` calls [`setindex!`](@ref)`(a,v,i)`.
* `a.b = c` calls [`setproperty!`](@ref)`(a,:b,c)`.
* Inside a function call, `f(a=b)` passes `b` as the value of keyword argument `a`.
* Inside parentheses with commas, `(a=1,)` constructs a [`NamedTuple`](@ref).
# Examples
Assigning `a` to `b` does not create a copy of `b`; instead use [`copy`](@ref) or [`deepcopy`](@ref).
```jldoctest
julia> b = [1]; a = b; b[1] = 2; a
1-element Array{Int64, 1}:
2
julia> b = [1]; a = copy(b); b[1] = 2; a
1-element Array{Int64, 1}:
1
```
Collections passed to functions are also not copied. Functions can modify (mutate) the contents of the objects their arguments refer to. (The names of functions which do this are conventionally suffixed with '!'.)
```jldoctest
julia> function f!(x); x[:] .+= 1; end
f! (generic function with 1 method)
julia> a = [1]; f!(a); a
1-element Array{Int64, 1}:
2
```
Assignment can operate on multiple variables in parallel, taking values from an iterable:
```jldoctest
julia> a, b = 4, 5
(4, 5)
julia> a, b = 1:3
1:3
julia> a, b
(1, 2)
```
Assignment can operate on multiple variables in series, and will return the value of the right-hand-most expression:
```jldoctest
julia> a = [1]; b = [2]; c = [3]; a = b = c
1-element Array{Int64, 1}:
3
julia> b[1] = 2; a, b, c
([2], [2], [2])
```
Assignment at out-of-bounds indices does not grow a collection. If the collection is a [`Vector`](@ref) it can instead be grown with [`push!`](@ref) or [`append!`](@ref).
```jldoctest
julia> a = [1, 1]; a[3] = 2
ERROR: BoundsError: attempt to access 2-element Array{Int64, 1} at index [3]
[...]
julia> push!(a, 2, 3)
4-element Array{Int64, 1}:
1
1
2
3
```
Assigning `[]` does not eliminate elements from a collection; instead use [`filter!`](@ref).
```jldoctest
julia> a = collect(1:3); a[a .<= 1] = []
ERROR: DimensionMismatch("tried to assign 0 elements to 1 destinations")
[...]
julia> filter!(x -> x > 1, a) # in-place & thus more efficient than a = a[a .> 1]
2-element Array{Int64, 1}:
2
3
```
"""
kw"="
"""
.=
Perform broadcasted assignment. The right-side argument is expanded as in
[`broadcast`](@ref) and then assigned into the left-side argument in-place.
Fuses with other dotted operators in the same expression; i.e. the whole
assignment expression is converted into a single loop.
`A .= B` is similar to `broadcast!(identity, A, B)`.
# Examples
```jldoctest
julia> A = zeros(4, 4); B = [1, 2, 3, 4];
julia> A .= B
4×4 Array{Float64, 2}:
1.0 1.0 1.0 1.0
2.0 2.0 2.0 2.0
3.0 3.0 3.0 3.0
4.0 4.0 4.0 4.0
julia> A
4×4 Array{Float64, 2}:
1.0 1.0 1.0 1.0
2.0 2.0 2.0 2.0
3.0 3.0 3.0 3.0
4.0 4.0 4.0 4.0
```
"""
kw".="
"""
.
The dot operator is used to access fields or properties of objects and access
variables defined inside modules.
In general, `a.b` calls `getproperty(a, :b)` (see [`getproperty`](@ref Base.getproperty)).
# Examples
```jldoctest
julia> z = 1 + 2im; z.im
2
julia> Iterators.product
product (generic function with 1 method)
```
"""
kw"."
"""
let
`let` statements create a new hard scope block and introduce new variable bindings
each time they run. Whereas assignments might reassign a new value to an existing value location,
`let` always creates a new location.
This difference is only detectable in the case of variables that outlive their scope via
closures. The `let` syntax accepts a comma-separated series of assignments and variable
names:
```julia
let var1 = value1, var2, var3 = value3
code
end
```
The assignments are evaluated in order, with each right-hand side evaluated in the scope
before the new variable on the left-hand side has been introduced. Therefore it makes
sense to write something like `let x = x`, since the two `x` variables are distinct and
have separate storage.
"""
kw"let"
"""
quote
`quote` creates multiple expression objects in a block without using the explicit
[`Expr`](@ref) constructor. For example:
```julia
ex = quote
x = 1
y = 2
x + y
end
```
Unlike the other means of quoting, `:( ... )`, this form introduces `QuoteNode` elements
to the expression tree, which must be considered when directly manipulating the tree.
For other purposes, `:( ... )` and `quote .. end` blocks are treated identically.
"""
kw"quote"
"""
{}
Curly braces are used to specify [type parameters](@ref man-parametric-types).
Type parameters allow a single type declaration to introduce a whole family of
new types — one for each possible combination of parameter values. For example,
the [`Set`](@ref) type describes many possible types of sets; it uses one type
parameter to describe the type of the elements it contains. The specific _parameterized_
types `Set{Float64}` and `Set{Int64}` describe two _concrete_ types: both are
subtypes ([`<:`](@ref)) of `Set`, but the former has `Float64` elements and the latter
has `Int64` elements.
"""
kw"{", kw"{}", kw"}"
"""
[]
Square braces are used for [indexing](@ref man-array-indexing), [indexed assignment](@ref man-indexed-assignment),
[array literals](@ref man-array-literals), and [array comprehensions](@ref man-comprehensions).
"""
kw"[", kw"[]", kw"]"
"""
()
Parentheses are used to group expressions, call functions, and construct [tuples](@ref Tuple) and [named tuples](@ref NamedTuple).
"""
kw"(", kw"()", kw")"
"""
#
The number sign (or hash) character is used to begin a single-line comment.
"""
kw"#"
"""
#= =#
A multi-line comment begins with `#=` and ends with `=#`, and may be nested.
"""
kw"#=", kw"=#"
"""
;
Semicolons are used as statement separators and mark the beginning of keyword arguments in function declarations or calls.
"""
kw";"
"""
Expr(head::Symbol, args...)
A type representing compound expressions in parsed julia code (ASTs).
Each expression consists of a `head` `Symbol` identifying which kind of
expression it is (e.g. a call, for loop, conditional statement, etc.),
and subexpressions (e.g. the arguments of a call).
The subexpressions are stored in a `Vector{Any}` field called `args`.
See the manual chapter on [Metaprogramming](@ref) and the developer
documentation [Julia ASTs](@ref).
# Examples
```jldoctest
julia> Expr(:call, :+, 1, 2)
:(1 + 2)
julia> dump(:(a ? b : c))
Expr
head: Symbol if
args: Array{Any}((3,))
1: Symbol a
2: Symbol b
3: Symbol c
```
"""
Expr
"""
\$
Interpolation operator for interpolating into e.g. [strings](@ref string-interpolation)
and [expressions](@ref man-expression-interpolation).
# Examples
```jldoctest
julia> name = "Joe"
"Joe"
julia> "My name is \$name."
"My name is Joe."
```
"""
kw"$"
"""
const
`const` is used to declare global variables whose values will not change. In almost all code
(and particularly performance sensitive code) global variables should be declared
constant in this way.
```julia
const x = 5
```
Multiple variables can be declared within a single `const`:
```julia
const y, z = 7, 11
```
Note that `const` only applies to one `=` operation, therefore `const x = y = 1`
declares `x` to be constant but not `y`. On the other hand, `const x = const y = 1`
declares both `x` and `y` constant.
Note that "constant-ness" does not extend into mutable containers; only the
association between a variable and its value is constant.
If `x` is an array or dictionary (for example) you can still modify, add, or remove elements.
In some cases changing the value of a `const` variable gives a warning instead of
an error.
However, this can produce unpredictable behavior or corrupt the state of your program,
and so should be avoided.
This feature is intended only for convenience during interactive use.
"""
kw"const"
"""
function
Functions are defined with the `function` keyword:
```julia
function add(a, b)
return a + b
end
```
Or the short form notation:
```julia
add(a, b) = a + b
```
The use of the [`return`](@ref) keyword is exactly the same as in other languages,
but is often optional. A function without an explicit `return` statement will return
the last expression in the function body.
"""
kw"function"
"""
return
`return x` causes the enclosing function to exit early, passing the given value `x`
back to its caller. `return` by itself with no value is equivalent to `return nothing`
(see [`nothing`](@ref)).
```julia
function compare(a, b)
a == b && return "equal to"
a < b ? "less than" : "greater than"
end
```
In general you can place a `return` statement anywhere within a function body, including
within deeply nested loops or conditionals, but be careful with `do` blocks. For
example:
```julia
function test1(xs)
for x in xs
iseven(x) && return 2x
end
end
function test2(xs)
map(xs) do x
iseven(x) && return 2x
x
end
end
```
In the first example, the return breaks out of `test1` as soon as it hits
an even number, so `test1([5,6,7])` returns `12`.
You might expect the second example to behave the same way, but in fact the `return`
there only breaks out of the *inner* function (inside the `do` block) and gives a value
back to `map`. `test2([5,6,7])` then returns `[5,12,7]`.
When used in a top-level expression (i.e. outside any function), `return` causes
the entire current top-level expression to terminate early.
"""
kw"return"
"""
if/elseif/else
`if`/`elseif`/`else` performs conditional evaluation, which allows portions of code to
be evaluated or not evaluated depending on the value of a boolean expression. Here is
the anatomy of the `if`/`elseif`/`else` conditional syntax:
```julia
if x < y
println("x is less than y")
elseif x > y
println("x is greater than y")
else
println("x is equal to y")
end
```
If the condition expression `x < y` is true, then the corresponding block is evaluated;
otherwise the condition expression `x > y` is evaluated, and if it is true, the
corresponding block is evaluated; if neither expression is true, the `else` block is
evaluated. The `elseif` and `else` blocks are optional, and as many `elseif` blocks as
desired can be used.
In contrast to some other languages conditions must be of type `Bool`. It does not
suffice for conditions to be convertible to `Bool`.
```jldoctest
julia> if 1 end
ERROR: TypeError: non-boolean (Int64) used in boolean context
```
"""
kw"if", kw"elseif", kw"else"
"""
a ? b : c
Short form for conditionals; read "if `a`, evaluate `b` otherwise evaluate `c`".
Also known as the [ternary operator](https://en.wikipedia.org/wiki/%3F:).
This syntax is equivalent to `if a; b else c end`, but is often used to
emphasize the value `b`-or-`c` which is being used as part of a larger
expression, rather than the side effects that evaluating `b` or `c` may have.
See the manual section on [control flow](@ref man-conditional-evaluation) for more details.
# Examples
```
julia> x = 1; y = 2;
julia> println(x > y ? "x is larger" : "y is larger")
y is larger
```
"""
kw"?", kw"?:"
"""
for
`for` loops repeatedly evaluate a block of statements while
iterating over a sequence of values.
# Examples
```jldoctest
julia> for i in [1, 4, 0]
println(i)
end
1
4
0
```
"""
kw"for"
"""
while
`while` loops repeatedly evaluate a conditional expression, and continue evaluating the
body of the while loop as long as the expression remains true. If the condition
expression is false when the while loop is first reached, the body is never evaluated.
# Examples
```jldoctest
julia> i = 1
1
julia> while i < 5
println(i)
global i += 1
end
1
2
3
4
```
"""
kw"while"
"""
end
`end` marks the conclusion of a block of expressions, for example
[`module`](@ref), [`struct`](@ref), [`mutable struct`](@ref),
[`begin`](@ref), [`let`](@ref), [`for`](@ref) etc.
`end` may also be used when indexing into an array to represent
the last index of a dimension.
# Examples
```jldoctest
julia> A = [1 2; 3 4]
2×2 Array{Int64, 2}:
1 2
3 4
julia> A[end, :]
2-element Array{Int64, 1}:
3
4
```
"""
kw"end"
"""
try/catch
A `try`/`catch` statement allows intercepting errors (exceptions) thrown
by [`throw`](@ref) so that program execution can continue.
For example, the following code attempts to write a file, but warns the user
and proceeds instead of terminating execution if the file cannot be written:
```julia
try
open("/danger", "w") do f
println(f, "Hello")
end
catch
@warn "Could not write file."
end
```
or, when the file cannot be read into a variable:
```julia
lines = try
open("/danger", "r") do f
readlines(f)
end
catch
@warn "File not found."
end
```
The syntax `catch e` (where `e` is any variable) assigns the thrown
exception object to the given variable within the `catch` block.
The power of the `try`/`catch` construct lies in the ability to unwind a deeply
nested computation immediately to a much higher level in the stack of calling functions.
"""
kw"try", kw"catch"
"""
finally
Run some code when a given block of code exits, regardless
of how it exits. For example, here is how we can guarantee that an opened file is
closed:
```julia
f = open("file")
try
operate_on_file(f)
finally
close(f)
end
```
When control leaves the [`try`](@ref) block (for example, due to a [`return`](@ref), or just finishing
normally), [`close(f)`](@ref) will be executed. If the `try` block exits due to an exception,
the exception will continue propagating. A `catch` block may be combined with `try` and
`finally` as well. In this case the `finally` block will run after `catch` has handled
the error.
"""
kw"finally"
"""
break
Break out of a loop immediately.
# Examples
```jldoctest
julia> i = 0
0
julia> while true
global i += 1
i > 5 && break
println(i)
end
1
2
3
4
5
```
"""
kw"break"
"""
continue
Skip the rest of the current loop iteration.
# Examples
```jldoctest
julia> for i = 1:6
iseven(i) && continue
println(i)
end
1
3
5
```
"""
kw"continue"
"""
do
Create an anonymous function and pass it as the first argument to
a function call.
For example:
```julia
map(1:10) do x
2x
end
```
is equivalent to `map(x->2x, 1:10)`.
Use multiple arguments like so:
```julia
map(1:10, 11:20) do x, y
x + y
end
```
"""
kw"do"
"""
...
The "splat" operator, `...`, represents a sequence of arguments.
`...` can be used in function definitions, to indicate that the function
accepts an arbitrary number of arguments.
`...` can also be used to apply a function to a sequence of arguments.
# Examples
```jldoctest
julia> add(xs...) = reduce(+, xs)
add (generic function with 1 method)
julia> add(1, 2, 3, 4, 5)
15
julia> add([1, 2, 3]...)
6
julia> add(7, 1:100..., 1000:1100...)
111107
```
"""
kw"..."
"""
;
`;` has a similar role in Julia as in many C-like languages, and is used to delimit the
end of the previous statement. `;` is not necessary after new lines, but can be used to
separate statements on a single line or to join statements into a single expression.
`;` is also used to suppress output printing in the REPL and similar interfaces.
# Examples
```julia
julia> function foo()
x = "Hello, "; x *= "World!"
return x
end
foo (generic function with 1 method)
julia> bar() = (x = "Hello, Mars!"; return x)
bar (generic function with 1 method)
julia> foo();
julia> bar()
"Hello, Mars!"
```
"""
kw";"
"""
x && y
Short-circuiting boolean AND.
"""
kw"&&"
"""
x || y
Short-circuiting boolean OR.
"""
kw"||"
"""
ccall((function_name, library), returntype, (argtype1, ...), argvalue1, ...)
ccall(function_name, returntype, (argtype1, ...), argvalue1, ...)
ccall(function_pointer, returntype, (argtype1, ...), argvalue1, ...)
Call a function in a C-exported shared library, specified by the tuple `(function_name, library)`,
where each component is either a string or symbol. Instead of specifying a library,
one can also use a `function_name` symbol or string, which is resolved in the current process.
Alternatively, `ccall` may also be used to call a function pointer `function_pointer`, such as one returned by `dlsym`.
Note that the argument type tuple must be a literal tuple, and not a tuple-valued
variable or expression.
Each `argvalue` to the `ccall` will be converted to the corresponding
`argtype`, by automatic insertion of calls to `unsafe_convert(argtype,
cconvert(argtype, argvalue))`. (See also the documentation for
[`unsafe_convert`](@ref Base.unsafe_convert) and [`cconvert`](@ref Base.cconvert) for further details.)
In most cases, this simply results in a call to `convert(argtype, argvalue)`.
"""
kw"ccall"
"""
llvmcall(fun_ir::String, returntype, Tuple{argtype1, ...}, argvalue1, ...)
llvmcall((mod_ir::String, entry_fn::String), returntype, Tuple{argtype1, ...}, argvalue1, ...)
llvmcall((mod_bc::Vector{UInt8}, entry_fn::String), returntype, Tuple{argtype1, ...}, argvalue1, ...)
Call the LLVM code provided in the first argument. There are several ways to specify this
first argument:
- as a literal string, representing function-level IR (similar to an LLVM `define` block),
with arguments are available as consecutive unnamed SSA variables (%0, %1, etc.);
- as a 2-element tuple, containing a string of module IR and a string representing the name
of the entry-point function to call;
- as a 2-element tuple, but with the module provided as an `Vector{UINt8}` with bitcode.
Note that contrary to `ccall`, the argument types must be specified as a tuple type, and not
a tuple of types. All types, as well as the LLVM code, should be specified as literals, and
not as variables or expressions (it may be necessary to use `@eval` to generate these
literals).