Add findfirst, findlast for searching char in strings

NEWS.md

@@ -20,6 +20,7 @@ Build system changes
 New library functions
 ---------------------
 
+* `findfirst`, `findlast`, `findnext` and `findprev` now addresses search for a character in a string ([#31664]).
 
 Standard library changes
 ------------------------

base/strings/search.jl

@@ -101,9 +101,29 @@ julia> findfirst("Julia", "JuliaLang")
 1:5
 ```
 """
-findfirst(pattern::AbstractString, string::AbstractString) =
+findfirst(pattern::AbstractString, string::AbstractString) = 
     findnext(pattern, string, firstindex(string))
 
+"""
+    findfirst(ch::Char, string::AbstractString)
+
+Find the first occurrence of `ch` in `string`. Equivalent to
+[`findfirst(isequal(ch), string)`](@ref).
+
+!!! compat "Julia 1.3"
+    This function requires at least Julia 1.3.
+
+# Examples
+```jldoctest
+julia> findfirst('a', "happy")
+2
+
+julia> findfirst('z', "happy") === nothing
+true
+```
+"""
+findfirst(ch::Char, string::AbstractString) = findfirst(==(ch), string)
+
 # AbstractString implementation of the generic findnext interface
 function findnext(testf::Function, s::AbstractString, i::Integer)
     z = ncodeunits(s) + 1
@@ -255,6 +275,25 @@ julia> findnext("Lang", "JuliaLang", 2)
 """
 findnext(t::AbstractString, s::AbstractString, i::Integer) = _search(s, t, i)
 
+"""
+    findnext(ch::Char, string::AbstractString, start::Integer)
+
+Find the next occurrence of `ch` in `string` starting at position `start`.
+
+!!! compat "Julia 1.3"
+    This function requires at least Julia 1.3.
+
+# Examples
+```jldoctest
+julia> findnext(`z`, "Hello to the world", 1) === nothing
+true
+
+julia> findnext(`o`, "Hello to the world", 6)
+8
+```
+"""
+findnext(ch::Char, string::AbstractString, ind::Integer) = findnext(==(ch), string, ind)
+
 """
     findlast(pattern::AbstractString, string::AbstractString)
 
@@ -273,6 +312,26 @@ julia> findfirst("Julia", "JuliaLang")
 findlast(pattern::AbstractString, string::AbstractString) =
     findprev(pattern, string, lastindex(string))
 
+"""
+    findlast(ch::Char, string::AbstractString)
+
+Find the last occurrence of `ch` in `string`. Equivalent to
+[`findlast(isequal(ch), string)`](@ref).
+
+!!! compat "Julia 1.3"
+    This function requires at least Julia 1.3.
+
+# Examples
+```jldoctest
+julia> findlast('p', "happy")
+4
+
+julia> findlast('z', "happy") === nothing
+true
+```
+"""
+findlast(ch::Char, string::AbstractString) = findlast(==(ch), string)
+
 # AbstractString implementation of the generic findprev interface
 function findprev(testf::Function, s::AbstractString, i::Integer)
     if i < 1
@@ -428,6 +487,25 @@ julia> findprev("Julia", "JuliaLang", 6)
 """
 findprev(t::AbstractString, s::AbstractString, i::Integer) = _rsearch(s, t, i)
 
+"""
+    findprev(ch::Char, string::AbstractString, start::Integer)
+
+Find the previous occurrence of `ch` in `string` starting at position `start`.
+
+!!! compat "Julia 1.3"
+    This function requires at least Julia 1.3.
+
+# Examples
+```jldoctest
+julia> findprev('z', "Hello to the world", 18) === nothing
+true
+
+julia> findprev('o', "Hello to the world", 18)
+15
+```
+"""
+findprev(ch::Char, string::AbstractString, ind::Integer) = findprev(==(ch), string, ind)
+
 """
     occursin(needle::Union{AbstractString,Regex,AbstractChar}, haystack::AbstractString)
 

test/strings/search.jl

@@ -24,41 +24,43 @@ end
 
 # ascii forward search
 for str in [astr, GenericString(astr)]
-    @test_throws BoundsError findnext(isequal('z'), str, 0)
-    @test_throws BoundsError findnext(isequal('∀'), str, 0)
-    @test findfirst(isequal('x'), str) == nothing
-    @test findfirst(isequal('\0'), str) == nothing
-    @test findfirst(isequal('\u80'), str) == nothing
-    @test findfirst(isequal('∀'), str) == nothing
-    @test findfirst(isequal('H'), str) == 1
-    @test findfirst(isequal('l'), str) == 3
-    @test findnext(isequal('l'), str, 4) == 4
-    @test findnext(isequal('l'), str, 5) == 11
-    @test findnext(isequal('l'), str, 12) == nothing
-    @test findfirst(isequal(','), str) == 6
-    @test findnext(isequal(','), str, 7) == nothing
-    @test findfirst(isequal('\n'), str) == 14
-    @test findnext(isequal('\n'), str, 15) == nothing
-    @test_throws BoundsError findnext(isequal('ε'), str, nextind(str,lastindex(str))+1)
-    @test_throws BoundsError findnext(isequal('a'), str, nextind(str,lastindex(str))+1)
+    @test_throws BoundsError findnext('z', str, 0)
+    @test_throws BoundsError findnext('∀', str, 0)
+    @test findfirst('x', str) == nothing
+    @test findfirst('\0', str) == nothing
+    @test findfirst('\u80', str) == nothing
+    @test findfirst('∀', str) == nothing
+    @test findfirst('H', str) == 1
+    @test findfirst('l', str) == 3
+    @test findfirst('e', str) == 2
+    @test findfirst('u', str) == nothing
+    @test findnext('l', str, 4) == 4
+    @test findnext('l', str, 5) == 11
+    @test findnext('l', str, 12) == nothing
+    @test findfirst(',', str) == 6
+    @test findnext(',', str, 7) == nothing
+    @test findfirst('\n', str) == 14
+    @test findnext('\n', str, 15) == nothing
+    @test_throws BoundsError findnext('ε', str, nextind(str,lastindex(str))+1)
+    @test_throws BoundsError findnext('a', str, nextind(str,lastindex(str))+1)
 end
 
 # ascii backward search
 for str in [astr]
-    @test findlast(isequal('x'), str) == nothing
-    @test findlast(isequal('\0'), str) == nothing
-    @test findlast(isequal('\u80'), str) == nothing
-    @test findlast(isequal('∀'), str) == nothing
-    @test findlast(isequal('H'), str) == 1
-    @test findprev(isequal('H'), str, 0) == nothing
-    @test findlast(isequal('l'), str) == 11
-    @test findprev(isequal('l'), str, 5) == 4
-    @test findprev(isequal('l'), str, 4) == 4
-    @test findprev(isequal('l'), str, 3) == 3
-    @test findprev(isequal('l'), str, 2) == nothing
-    @test findlast(isequal(','), str) == 6
-    @test findprev(isequal(','), str, 5) == nothing
-    @test findlast(isequal('\n'), str) == 14
+    @test findlast('x', str) == nothing
+    @test findlast('\0', str) == nothing
+    @test findlast('\u80', str) == nothing
+    @test findlast('∀', str) == nothing
+    @test findlast('H', str) == 1
+    @test findprev('H', str, 0) == nothing
+    @test findlast('l', str) == 11
+    @test findprev('l', str, 5) == 4
+    @test findprev('l', str, 4) == 4
+    @test findprev('l', str, 3) == 3
+    @test findprev('l', str, 2) == nothing
+    @test findlast(',', str) == 6
+    @test findprev(',', str, 5) == nothing
+    @test findlast('\n', str) == 14
 end
 
 # utf-8 forward search