From 3ddbd0ad1d3d512c16a3c5364aadc8b4334a83d4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Mon, 2 Oct 2017 09:57:04 +0200
Subject: [PATCH 1/5] first and last with nchar

---
 NEWS.md                   |  6 ++++-
 base/strings/basic.jl     | 47 +++++++++++++++++++++++++++++++++++++++
 doc/src/stdlib/strings.md |  2 ++
 test/strings/basic.jl     | 20 +++++++++++++++++
 4 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index 4419d4d7f67e9..0f9df2e7f22ae 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -236,8 +236,12 @@ This section lists changes that do not have deprecation warnings.
 Library improvements
 --------------------
 
+  * Functions `first` and `last` now accept `nchar` argument for `AbstractString`.
+    If this argument is used they reutrn a substring consisting of first/last `nchar`
+    characters from the original string ([#?????]).
+
   * The functions `nextind` and `prevind` now accept `nchar` argument that indicates
-    number of characters to move ([#23805]).
+    the number of characters to move ([#23805]).
 
   * The functions `strip`, `lstrip` and `rstrip` now return `SubString` ([#22496]).
 
diff --git a/base/strings/basic.jl b/base/strings/basic.jl
index c6c572882ce66..718a34b5b89a1 100644
--- a/base/strings/basic.jl
+++ b/base/strings/basic.jl
@@ -610,3 +610,50 @@ function filter(f, s::AbstractString)
     end
     String(take!(out))
 end
+
+## string first and last ##
+
+"""
+    first(str::AbstractString, nchar::Integer)
+
+Get a string consisting of first `nchar` characters of `str`.
+
+```jldoctest
+julia> first("∀ϵ≠0: ϵ²>0", 0)
+""
+
+julia> first("∀ϵ≠0: ϵ²>0", 1)
+"∀"
+
+julia> first("∀ϵ≠0: ϵ²>0", 3)
+"∀ϵ≠"
+```
+"""
+function first(str::AbstractString, nchar::Integer)
+    nchar == 0 && return ""
+    nchar == 1 && return str[1:1]
+    str[1:nextind(str, 1, nchar-1)]
+end
+
+"""
+    last(str::AbstractString, nchar::Integer)
+
+Get a string consisting of last `nchar` characters of `str`.
+
+```jldoctest
+julia> last("∀ϵ≠0: ϵ²>0", 0)
+""
+
+julia> last("∀ϵ≠0: ϵ²>0", 1)
+"0"
+
+julia> last("∀ϵ≠0: ϵ²>0", 3)
+"²>0"
+```
+"""
+function last(str::AbstractString, nchar::Integer)
+    nchar == 0 && return ""
+    e = endof(str)
+    nchar == 1 && return str[e:e]
+    str[prevind(str, e, nchar-1):e]
+end
diff --git a/doc/src/stdlib/strings.md b/doc/src/stdlib/strings.md
index 003b9b1b92b6d..2d00e04bbe39b 100644
--- a/doc/src/stdlib/strings.md
+++ b/doc/src/stdlib/strings.md
@@ -46,6 +46,8 @@ Base.lstrip
 Base.rstrip
 Base.startswith
 Base.endswith
+Base.first(::AbstractString, ::Integer)
+Base.last(::AbstractString, ::Integer)
 Base.uppercase
 Base.lowercase
 Base.titlecase
diff --git a/test/strings/basic.jl b/test/strings/basic.jl
index 2da583f9474b5..33719b3507384 100644
--- a/test/strings/basic.jl
+++ b/test/strings/basic.jl
@@ -623,3 +623,23 @@ end
         @test prevind(strs[2], -1, 1) == 0
     end
 end
+
+@testset "first and last" begin
+    s = "∀ϵ≠0: ϵ²>0"
+    @test_throws ArgumentError first(s, -1)
+    @test first(s, 0) == ""
+    @test first(s, 1) == "∀"
+    @test first(s, 2) == "∀ϵ"
+    @test first(s, 3) == "∀ϵ≠"
+    @test first(s, 4) == "∀ϵ≠0"
+    @test first(s, length(s)) == s
+    @test_throws BoundsError first(s, length(s)+1)
+    @test_throws ArgumentError last(s, -1)
+    @test last(s, 0) == ""
+    @test last(s, 1) == "0"
+    @test last(s, 2) == ">0"
+    @test last(s, 3) == "²>0"
+    @test last(s, 4) == "ϵ²>0"
+    @test last(s, length(s)) == s
+    @test_throws BoundsError last(s, length(s)+1)
+end

From df78dbe70e636c7426a4ae27a35c79d2e958f2a4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Mon, 2 Oct 2017 10:40:30 +0200
Subject: [PATCH 2/5] improve description

---
 NEWS.md               | 2 +-
 base/strings/basic.jl | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index 0f9df2e7f22ae..f8bc36b15355e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -237,7 +237,7 @@ Library improvements
 --------------------
 
   * Functions `first` and `last` now accept `nchar` argument for `AbstractString`.
-    If this argument is used they reutrn a substring consisting of first/last `nchar`
+    If this argument is used they reutrn a string consisting of first/last `nchar`
     characters from the original string ([#?????]).
 
   * The functions `nextind` and `prevind` now accept `nchar` argument that indicates
diff --git a/base/strings/basic.jl b/base/strings/basic.jl
index 718a34b5b89a1..dc6a8257479ba 100644
--- a/base/strings/basic.jl
+++ b/base/strings/basic.jl
@@ -616,7 +616,7 @@ end
 """
     first(str::AbstractString, nchar::Integer)
 
-Get a string consisting of first `nchar` characters of `str`.
+Get a string consisting of the first `nchar` characters of `str`.
 
 ```jldoctest
 julia> first("∀ϵ≠0: ϵ²>0", 0)
@@ -638,7 +638,7 @@ end
 """
     last(str::AbstractString, nchar::Integer)
 
-Get a string consisting of last `nchar` characters of `str`.
+Get a string consisting of the last `nchar` characters of `str`.
 
 ```jldoctest
 julia> last("∀ϵ≠0: ϵ²>0", 0)

From b6d7e9f7c5a787636337842c18099b36250a6721 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Mon, 2 Oct 2017 10:42:09 +0200
Subject: [PATCH 3/5] add PR number

---
 NEWS.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index f8bc36b15355e..bf492b68b2d78 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -238,7 +238,7 @@ Library improvements
 
   * Functions `first` and `last` now accept `nchar` argument for `AbstractString`.
     If this argument is used they reutrn a string consisting of first/last `nchar`
-    characters from the original string ([#?????]).
+    characters from the original string ([#23960]).
 
   * The functions `nextind` and `prevind` now accept `nchar` argument that indicates
     the number of characters to move ([#23805]).

From 68098d2a234807b1954fe887a7e74a540db3fa9d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Mon, 2 Oct 2017 10:51:53 +0200
Subject: [PATCH 4/5] fix typo

---
 NEWS.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index bf492b68b2d78..744c302b85d5f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -237,7 +237,7 @@ Library improvements
 --------------------
 
   * Functions `first` and `last` now accept `nchar` argument for `AbstractString`.
-    If this argument is used they reutrn a string consisting of first/last `nchar`
+    If this argument is used they return a string consisting of first/last `nchar`
     characters from the original string ([#23960]).
 
   * The functions `nextind` and `prevind` now accept `nchar` argument that indicates

From 9fbb56803451a4e9e8798a40b1951a81ce98b99e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Mon, 2 Oct 2017 11:26:30 +0200
Subject: [PATCH 5/5] make first/last type stable

---
 base/strings/basic.jl | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/base/strings/basic.jl b/base/strings/basic.jl
index dc6a8257479ba..52c1a32c1eee9 100644
--- a/base/strings/basic.jl
+++ b/base/strings/basic.jl
@@ -630,8 +630,9 @@ julia> first("∀ϵ≠0: ϵ²>0", 3)
 ```
 """
 function first(str::AbstractString, nchar::Integer)
-    nchar == 0 && return ""
-    nchar == 1 && return str[1:1]
+    if 0 <= nchar <= 1
+        return str[1:nchar]
+    end
     str[1:nextind(str, 1, nchar-1)]
 end
 
@@ -652,8 +653,9 @@ julia> last("∀ϵ≠0: ϵ²>0", 3)
 ```
 """
 function last(str::AbstractString, nchar::Integer)
-    nchar == 0 && return ""
     e = endof(str)
-    nchar == 1 && return str[e:e]
+    if 0 <= nchar <= 1
+        return str[(e-nchar+1):e]
+    end
     str[prevind(str, e, nchar-1):e]
 end