isAlphaNumberic and isDigit improvement + tests (#6579)

if we encounter a character that does not satisfy the proc, we return immediately, without continuing to loop over the rest of the chars in the string.

lib/pure/strutils.nim

@@ -138,7 +138,8 @@ proc isAlphaNumeric*(s: string): bool {.noSideEffect, procvar,
 
   result = true
   for c in s:
-    result = c.isAlphaNumeric() and result
+    if not c.isAlphaNumeric():
+      return false
 
 proc isDigit*(s: string): bool {.noSideEffect, procvar,
   rtl, extern: "nsuIsDigitStr".}=
@@ -153,7 +154,8 @@ proc isDigit*(s: string): bool {.noSideEffect, procvar,
 
   result = true
   for c in s:
-    result = c.isDigit() and result
+    if not c.isDigit():
+      return false
 
 proc isSpaceAscii*(s: string): bool {.noSideEffect, procvar,
   rtl, extern: "nsuIsSpaceAsciiStr".}=

tests/stdlib/tstrutil.nim

@@ -64,6 +64,25 @@ proc testDelete =
   delete(s, 0, 0)
   assert s == "1236789ABCDEFG"
 
+
+proc testIsAlphaNumeric =
+  assert isAlphaNumeric("abcdABC1234") == true
+  assert isAlphaNumeric("a") == true
+  assert isAlphaNumeric("abcABC?1234") == false
+  assert isAlphaNumeric("abcABC 1234") == false
+  assert isAlphaNumeric(".") == false
+
+testIsAlphaNumeric()
+
+proc testIsDigit =
+  assert isDigit("1") == true
+  assert isDigit("1234") == true
+  assert isDigit("abcABC?1234") == false
+  assert isDigit(".") == false
+  assert isDigit(":") == false
+
+testIsDigit()
+
 proc testFind =
   assert "0123456789ABCDEFGH".find('A') == 10
   assert "0123456789ABCDEFGH".find('A', 5) == 10