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nullable.jl
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nullable.jl
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# This file is a part of Julia. License is MIT: https://julialang.org/license
immutable NullException <: Exception
end
Nullable{T}(value::T, isnull::Bool=false) = Nullable{T}(value, isnull)
Nullable() = Nullable{Union{}}()
eltype{T}(::Type{Nullable{T}}) = T
convert{T}(::Type{Nullable{T}}, x::Nullable{T}) = x
convert( ::Type{Nullable }, x::Nullable ) = x
convert{T}(t::Type{Nullable{T}}, x::Any) = convert(t, convert(T, x))
function convert{T}(::Type{Nullable{T}}, x::Nullable)
return isnull(x) ? Nullable{T}() : Nullable{T}(convert(T, get(x)))
end
convert{T}(::Type{Nullable{T}}, x::T) = Nullable{T}(x)
convert{T}(::Type{Nullable }, x::T) = Nullable{T}(x)
convert{T}(::Type{Nullable{T}}, ::Void) = Nullable{T}()
convert( ::Type{Nullable }, ::Void) = Nullable{Union{}}()
promote_rule{S,T}(::Type{Nullable{S}}, ::Type{T}) = Nullable{promote_type(S, T)}
promote_rule{S,T}(::Type{Nullable{S}}, ::Type{Nullable{T}}) = Nullable{promote_type(S, T)}
promote_op{S,T}(op::Any, ::Type{Nullable{S}}, ::Type{Nullable{T}}) = Nullable{promote_op(op, S, T)}
function show{T}(io::IO, x::Nullable{T})
if get(io, :compact, false)
if isnull(x)
print(io, "#NULL")
else
show(io, x.value)
end
else
print(io, "Nullable{")
showcompact(io, eltype(x))
print(io, "}(")
if !isnull(x)
showcompact(io, x.value)
end
print(io, ')')
end
end
"""
get(x::Nullable[, y])
Attempt to access the value of `x`. Returns the value if it is present;
otherwise, returns `y` if provided, or throws a `NullException` if not.
"""
@inline function get{S,T}(x::Nullable{S}, y::T)
if isbits(S)
ifelse(x.isnull, y, x.value)
else
x.isnull ? y : x.value
end
end
get(x::Nullable) = x.isnull ? throw(NullException()) : x.value
isnull(x::Nullable) = x.isnull
function isequal(x::Nullable, y::Nullable)
if x.isnull && y.isnull
return true
elseif x.isnull || y.isnull
return false
else
return isequal(x.value, y.value)
end
end
==(x::Nullable, y::Nullable) = throw(NullException())
const nullablehash_seed = UInt === UInt64 ? 0x932e0143e51d0171 : 0xe51d0171
function hash(x::Nullable, h::UInt)
if x.isnull
return h + nullablehash_seed
else
return hash(x.value, h + nullablehash_seed)
end
end