Add head and tail arguments to chop

NEWS.md

@@ -252,6 +252,9 @@ This section lists changes that do not have deprecation warnings.
 Library improvements
 --------------------
 
+  * The function `chop` now accepts two arguments `head` and `tail` allowing to specify
+    number of characters to remove from the head and tail of the string ([#24126]).
+
   * Functions `first` and `last` now accept `nchar` argument for `AbstractString`.
     If this argument is used they return a string consisting of first/last `nchar`
     characters from the original string ([#23960]).

base/strings/util.jl

@@ -66,9 +66,12 @@ startswith(a::Vector{UInt8}, b::Vector{UInt8}) =
 # TODO: fast endswith
 
 """
-    chop(s::AbstractString)
+    chop(s::AbstractString, head::Integer=0, tail::Integer=1)
 
-Remove the last character from `s`.
+Remove the first `head` and the last `tail` characters from `s`.
+The call `chop(s)` removes the last character from `s`.
+If it is requested to remove more characters than `length(s)`
+then an empty string is returned.
 
 # Examples
 ```jldoctest
@@ -77,9 +80,23 @@ julia> a = "March"
 
 julia> chop(a)
 "Marc"
+
+julia> chop(a, 1, 2)
+"ar"
+
+julia> chop(a, 5, 5)
+""
 ```
 """
-chop(s::AbstractString) = SubString(s, 1, prevind(s, endof(s)))
+function chop(s::AbstractString, head::Integer, tail::Integer)
+    # negative values of head/tail will throw error in nextind/prevind
+    headidx = head == 0 ? start(s) : nextind(s, start(s), head)
+    tailidx = tail == 0 ? endof(s) : prevind(s, endof(s), tail)
+    SubString(s, headidx, tailidx)
+end
+
+# no head/tail version left for performance reasons
+chop(s::AbstractString) = SubString(s, start(s), prevind(s, endof(s)))
 
 """
     chomp(s::AbstractString)

test/strings/util.jl

@@ -231,10 +231,30 @@ end
 @testset "chomp/chop" begin
     @test chomp("foo\n") == "foo"
     @test chomp("fo∀\n") == "fo∀"
+    @test chomp("foo\r\n") == "foo"
+    @test chomp("fo∀\r\n") == "fo∀"
     @test chomp("fo∀") == "fo∀"
     @test chop("fooε") == "foo"
     @test chop("foεo") == "foε"
     @test chop("∃∃∃∃") == "∃∃∃"
+    @test chop("∀ϵ∃Δ", 0, 0) == "∀ϵ∃Δ"
+    @test chop("∀ϵ∃Δ", 0, 1) == "∀ϵ∃"
+    @test chop("∀ϵ∃Δ", 0, 2) == "∀ϵ"
+    @test chop("∀ϵ∃Δ", 0, 3) == "∀"
+    @test chop("∀ϵ∃Δ", 0, 4) == ""
+    @test chop("∀ϵ∃Δ", 0, 5) == ""
+    @test chop("∀ϵ∃Δ", 1, 0) == "ϵ∃Δ"
+    @test chop("∀ϵ∃Δ", 2, 0) == "∃Δ"
+    @test chop("∀ϵ∃Δ", 3, 0) == "Δ"
+    @test chop("∀ϵ∃Δ", 4, 0) == ""
+    @test chop("∀ϵ∃Δ", 5, 0) == ""
+    @test chop("∀ϵ∃Δ", 1, 1) == "ϵ∃"
+    @test chop("∀ϵ∃Δ", 2, 2) == ""
+    @test chop("∀ϵ∃Δ", 3, 3) == ""
+    @test_throws ArgumentError chop("∀ϵ∃Δ", -3, 3)
+    @test_throws ArgumentError chop("∀ϵ∃Δ", 3, -3)
+    @test_throws ArgumentError chop("∀ϵ∃Δ", -3, -3)
+
     @test isa(chomp("foo"), SubString)
     @test isa(chop("foo"), SubString)
 end