Accept AbstractChar in count and findall (::Char, ::String) (JuliaLan…

…g#38675)

This change solves an issue raised in this post, in which searching for a char in a string results in a Method error: https://discourse.julialang.org/t/method-for-counting-characters-in-string-count-a-batman-vs-count-a-batman/51153

Co-authored-by: Stefan Karpinski <[email protected]>
Co-authored-by: Steven G. Johnson <[email protected]>

NEWS.md

@@ -3,7 +3,7 @@ Julia v1.7 Release Notes
 
 New language features
 ---------------------
-
+* `count` and `findall` now accept an `AbstractChar` argument to search for a character in a string ([#38675]).
 
 Language changes
 ----------------

base/regex.jl

@@ -396,9 +396,29 @@ function findall(t::Union{AbstractString,AbstractPattern}, s::AbstractString; ov
  return found
 end
 
+"""
+ findall(c::AbstractChar, s::AbstractString)
+
+Return a vector `I` of the indices of `s` where `s[i] == c`. If there are no such
+elements in `s`, return an empty array.
+
+# Examples
+```jldoctest
+julia> findall('a', "batman")
+2-element Vector{Int64}:
+ 2
+ 5
+```
+
+!!! compat "Julia 1.7"
+ This method requires at least Julia 1.7.
+"""
+findall(c::AbstractChar, s::AbstractString) = findall(isequal(c),s)
+
+
 """
  count(
- pattern::Union{AbstractString,AbstractPattern},
+ pattern::Union{AbstractChar,AbstractString,AbstractPattern},
  string::AbstractString;
  overlap::Bool = false,
  )
@@ -411,8 +431,11 @@ original string, otherwise they must be from disjoint character ranges.
 
 !!! compat "Julia 1.3"
  This method requires at least Julia 1.3.
+
+!!! compat "Julia 1.7"
+ Using a character as the pattern requires at least Julia 1.7.
 """
-function count(t::Union{AbstractString,AbstractPattern}, s::AbstractString; overlap::Bool=false)
+function count(t::Union{AbstractChar,AbstractString,AbstractPattern}, s::AbstractString; overlap::Bool=false)
  n = 0
  i, e = firstindex(s), lastindex(s)
  while true

test/regex.jl

@@ -64,12 +64,22 @@
  @test findall(r"\w+", "foo bar", overlap=true) == [1:3, 2:3, 3:3, 5:7, 6:7, 7:7]
  @test all(findall(r"\w*", "foo bar") .=== [1:3, 4:3, 5:7, 8:7]) # use === to compare empty ranges
  @test all(findall(r"\b", "foo bar") .=== [1:0, 4:3, 5:4, 8:7]) # use === to compare empty ranges
+ # with Char as argument
+ @test findall('a', "batman") == [2, 5]
+ @test findall('→', "OH⁻ + H₃CBr → HOH₃CBr⁻ → HOCH₃ + Br⁻") == [17, 35]
+ @test findall('a', "") == Int[]
+ @test findall('c', "batman") == Int[]
 
  # count
  @test count(r"\w+", "foo bar") == 2
  @test count(r"\w+", "foo bar", overlap=true) == 6
  @test count(r"\w*", "foo bar") == 4
  @test count(r"\b", "foo bar") == 4
+ # count with char as argument
+ @test count('a', "batman") == 2
+ @test count('a', "aaa", overlap=true) == 3
+ @test count('a', "") == 0
+ @test count('→', "OH⁻ + H₃CBr → (HOH₃CBr⁻)† → HOCH₃ + Br⁻") == 2
 
  # Unnamed subpatterns
  let m = match(r"(.)(.)(.)", "xyz")