Allow removing an AbstractChar with chopprefix/chopsuffix (JuliaLang#59425)

Author: ararslan

NEWS.md

@@ -63,6 +63,7 @@ New library features
 * `sort(keys(::Dict))` and `sort(values(::Dict))` now automatically collect, they previously threw ([#56978]).
 * `Base.AbstractOneTo` is added as a supertype of one-based axes, with `Base.OneTo` as its subtype ([#56902]).
 * `takestring!(::IOBuffer)` removes the content from the buffer, returning the content as a `String`.
+* `chopprefix` and `chopsuffix` can now also accept an `AbstractChar` as the prefix/suffix to remove.
 * The `macroexpand` (with default true) and the new `macroexpand!` (with default false)
   functions now support a `legacyscope` boolean keyword argument to control whether to run
   the legacy scope resolution pass over the result. The legacy scope resolution code has

base/strings/util.jl

@@ -232,7 +232,7 @@ end
 # chop(s::AbstractString) = SubString(s, firstindex(s), prevind(s, lastindex(s)))
 
 """
-    chopprefix(s::AbstractString, prefix::Union{AbstractString,Regex})::SubString
+    chopprefix(s::AbstractString, prefix::Union{AbstractString,Regex,AbstractChar})::SubString
 
 Remove the prefix `prefix` from `s`. If `s` does not start with `prefix`, a string equal to `s` is returned.
 
@@ -241,6 +241,9 @@ See also [`chopsuffix`](@ref).
 !!! compat "Julia 1.8"
     This function is available as of Julia 1.8.
 
+!!! compat "Julia 1.13"
+    The method which accepts an `AbstractChar` prefix is available as of Julia 1.13.
+
 # Examples
 ```jldoctest
 julia> chopprefix("Hamburger", "Ham")
@@ -272,8 +275,16 @@ function chopprefix(s::Union{String, SubString{String}},
     end
 end
 
+function chopprefix(s::AbstractString, prefix::AbstractChar)
+    if !isempty(s) && first(s) == prefix
+        return SubString(s, nextind(s, firstindex(s)))
+    else
+        return SubString(s)
+    end
+end
+
 """
-    chopsuffix(s::AbstractString, suffix::Union{AbstractString,Regex})::SubString
+    chopsuffix(s::AbstractString, suffix::Union{AbstractString,Regex,AbstractChar})::SubString
 
 Remove the suffix `suffix` from `s`. If `s` does not end with `suffix`, a string equal to `s` is returned.
 
@@ -282,6 +293,9 @@ See also [`chopprefix`](@ref).
 !!! compat "Julia 1.8"
     This function is available as of Julia 1.8.
 
+!!! compat "Julia 1.13"
+    The method which accepts an `AbstractChar` suffix is available as of Julia 1.13.
+
 # Examples
 ```jldoctest
 julia> chopsuffix("Hamburger", "er")
@@ -315,6 +329,13 @@ function chopsuffix(s::Union{String, SubString{String}},
     end
 end
 
+function chopsuffix(s::AbstractString, suffix::AbstractChar)
+    if !isempty(s) && last(s) == suffix
+        return SubString(s, firstindex(s), prevind(s, lastindex(s)))
+    else
+        return SubString(s)
+    end
+end
 
 """
     chomp(s::AbstractString)::SubString

test/strings/util.jl

@@ -709,6 +709,11 @@ end
 
         @test isa(chopprefix(S("foo"), "fo"), SubString)
         @test isa(chopsuffix(S("foo"), "oo"), SubString)
+
+        @test chopprefix(S(""), 'z') == chopsuffix(S(""), 'z') == ""
+        @test chopprefix(S("吃齋"), '🍖') == chopsuffix(S("吃齋"), '🍖') == "吃齋"
+        @test chopprefix(S("äwesome"), 'ä') == "wesome"
+        @test chopsuffix(S("äwesome"), 'e') == "äwesom"
     end
 end