default last in strutils.find to -1

changelog.md

@@ -79,6 +79,12 @@
 
 - `strformat` is now part of `include std/prelude`.
 
+- Changed the behavior of passing `last=0` to any overload of `strutils.find`.
+  Previously, `last=0` indicated to search to the end of the string. Now,
+  `last=0` means "search as far as the 0th index of the string." Use `last = -1`
+  to use the old behavior. No change is required for invocations of
+  `strutils.find` where `last` is unspecified.
+
 - Deprecated `proc reversed*[T](a: openArray[T], first: Natural, last: int): seq[T]` in `std/algorithm`.
 
 - The configuration subsystem now allows for `-d:release` and `-d:danger` to work as expected.

lib/pure/strutils.nim

@@ -1784,15 +1784,15 @@ func initSkipTable*(a: var SkipTable, sub: string) {.rtl,
   for i in 0 ..< m - 1:
     a[sub[i]] = m - 1 - i
 
-func find*(a: SkipTable, s, sub: string, start: Natural = 0, last = 0): int {.
+func find*(a: SkipTable, s, sub: string, start: Natural = 0, last = -1): int {.
     rtl, extern: "nsuFindStrA".} =
   ## Searches for `sub` in `s` inside range `start..last` using preprocessed
-  ## table `a`. If `last` is unspecified, it defaults to `s.high` (the last
+  ## table `a`. If `last` is negative, it defaults to `s.high` (the last
   ## element).
   ##
   ## Searching is case-sensitive. If `sub` is not in `s`, -1 is returned.
   let
-    last = if last == 0: s.high else: last
+    last = if last < 0: s.high else: last
     subLast = sub.len - 1
 
   if subLast == -1:
@@ -1823,10 +1823,10 @@ when not (defined(js) or defined(nimdoc) or defined(nimscript)):
 else:
   const hasCStringBuiltin = false
 
-func find*(s: string, sub: char, start: Natural = 0, last = 0): int {.rtl,
+func find*(s: string, sub: char, start: Natural = 0, last = -1): int {.rtl,
     extern: "nsuFindChar".} =
   ## Searches for `sub` in `s` inside range `start..last` (both ends included).
-  ## If `last` is unspecified, it defaults to `s.high` (the last element).
+  ## If `last` is negative, it defaults to `s.high` (the last element).
   ##
   ## Searching is case-sensitive. If `sub` is not in `s`, -1 is returned.
   ## Otherwise the index returned is relative to `s[0]`, not `start`.
@@ -1835,7 +1835,7 @@ func find*(s: string, sub: char, start: Natural = 0, last = 0): int {.rtl,
   ## See also:
   ## * `rfind func<#rfind,string,char,Natural>`_
   ## * `replace func<#replace,string,char,char>`_
-  let last = if last == 0: s.high else: last
+  let last = if last < 0: s.high else: last
   when nimvm:
     for i in int(start)..last:
       if sub == s[i]: return i
@@ -1851,10 +1851,10 @@ func find*(s: string, sub: char, start: Natural = 0, last = 0): int {.rtl,
         if sub == s[i]: return i
   return -1
 
-func find*(s: string, chars: set[char], start: Natural = 0, last = 0): int {.
+func find*(s: string, chars: set[char], start: Natural = 0, last = -1): int {.
     rtl, extern: "nsuFindCharSet".} =
   ## Searches for `chars` in `s` inside range `start..last` (both ends included).
-  ## If `last` is unspecified, it defaults to `s.high` (the last element).
+  ## If `last` is negative, it defaults to `s.high` (the last element).
   ##
   ## If `s` contains none of the characters in `chars`, -1 is returned.
   ## Otherwise the index returned is relative to `s[0]`, not `start`.
@@ -1863,15 +1863,15 @@ func find*(s: string, chars: set[char], start: Natural = 0, last = 0): int {.
   ## See also:
   ## * `rfind func<#rfind,string,set[char],Natural>`_
   ## * `multiReplace func<#multiReplace,string,varargs[]>`_
-  let last = if last == 0: s.high else: last
+  let last = if last < 0: s.high else: last
   for i in int(start)..last:
     if s[i] in chars: return i
   return -1
 
-func find*(s, sub: string, start: Natural = 0, last = 0): int {.rtl,
+func find*(s, sub: string, start: Natural = 0, last = -1): int {.rtl,
     extern: "nsuFindStr".} =
   ## Searches for `sub` in `s` inside range `start..last` (both ends included).
-  ## If `last` is unspecified, it defaults to `s.high` (the last element).
+  ## If `last` is negative, it defaults to `s.high` (the last element).
   ##
   ## Searching is case-sensitive. If `sub` is not in `s`, -1 is returned.
   ## Otherwise the index returned is relative to `s[0]`, not `start`.
@@ -1880,6 +1880,12 @@ func find*(s, sub: string, start: Natural = 0, last = 0): int {.rtl,
   ## See also:
   ## * `rfind func<#rfind,string,string,Natural>`_
   ## * `replace func<#replace,string,string,string>`_
+  runnableExamples:
+    doAssert find("abcbc", "") == 0
+    doAssert find("abcbc", "bc") == 1
+    doAssert find("abcbc", "bc", start=2) == 3
+    doAssert find("abcbc", "bc", last = 2) == 1
+    doAssert find("abcbc", "bc", last = 1) == -1
   if sub.len > s.len - start: return -1
   if sub.len == 1: return find(s, sub[0], start, last)
 
@@ -1895,7 +1901,7 @@ func find*(s, sub: string, start: Natural = 0, last = 0): int {.rtl,
       useSkipTable()
     else:
       when hasCStringBuiltin:
-        if last == 0 and s.len > start:
+        if last < 0 and s.len > start:
           let found = c_strstr(s[start].unsafeAddr, sub)
           if not found.isNil:
             result = cast[ByteAddress](found) -% cast[ByteAddress](s.cstring)

tests/stdlib/tstrutils.nim

@@ -267,15 +267,15 @@ template main() =
     # when last <= start, searching for non-empty string
     block:
       let last: int = -1
-      doAssert "abcd".find("ab", start=0, last=last) == -1
+      doAssert "abcd".find("ab", start=0, last=last) == 0
       doAssert "abcd".find("ab", start=1, last=last) == -1
-      doAssert "abcd".find("bc", start=1, last=last) == -1
+      doAssert "abcd".find("bc", start=1, last=last) == 1
       doAssert "abcd".find("bc", start=2, last=last) == -1
     block:
       let last: int = 0
-      doAssert "abcd".find("ab", start=0, last=last) == 0
+      doAssert "abcd".find("ab", start=0, last=last) == -1
       doAssert "abcd".find("ab", start=1, last=last) == -1
-      doAssert "abcd".find("bc", start=1, last=last) == 1
+      doAssert "abcd".find("bc", start=1, last=last) == -1
       doAssert "abcd".find("bc", start=2, last=last) == -1
     block:
       let last: int = 1