Improve replacement performance

src/nre.nim

@@ -443,7 +443,8 @@ proc replace*(str: string, pattern: Regex,
 
 proc replace*(str: string, pattern: Regex, sub: string): string =
   return str.replace(pattern, proc (match: RegexMatch): string =
-    sub % match.captures.toSeq )
+    # - 1 because the string numbers are 0-indexed
+    formatStr(sub, match.captures[name], match.captures[id - 1]) )
 
 # }}}
 

src/private/util.nim

@@ -5,3 +5,50 @@ proc fget*[K, V](self: Table[K, V], key: K): V =
     return self[key]
   else:
     raise newException(KeyError, "Key does not exist in table: " & $key)
+
+const Ident = {'a'..'z', 'A'..'Z', '0'..'9', '_', '\128'..'\255'}
+const StartIdent = Ident - {'0'..'9'}
+
+template formatStr*(howExpr, namegetter, idgetter: expr): expr =
+  let how = howExpr
+  result = newStringOfCap(how.len)
+  var i = 0
+  var lastNum = 1
+
+  while i < how.len:
+    if how[i] != '$':
+      result.add(how[i])
+      i += 1
+    elif how[i + 1] == '$':
+      result.add('$')
+      i += 2
+    elif how[i + 1] == '#':
+      var id {.inject.} = lastNum
+      result.add(idgetter)
+      lastNum += 1
+      i += 2
+    elif how[i + 1] in {'0'..'9'}:
+      i += 1
+      var id {.inject.} = 0
+      while i < how.len and how[i] in {'0'..'9'}:
+        id += (id * 10) + (ord(how[i]) - ord('0'))
+        i += 1
+      result.add(idgetter)
+      lastNum = id + 1
+    elif how[i + 1] in StartIdent:
+      i += 1
+      var name {.inject.} = ""
+      while i < how.len and how[i] in Ident:
+        name.add(how[i])
+        i += 1
+      result.add(namegetter)
+    elif how[i + 1] == '{':
+      i += 2
+      var name {.inject.} = ""
+      while i < how.len and how[i] != '}':
+        name.add(how[i])
+        i += 1
+      i += 1
+      result.add(namegetter)
+    else:
+      raise newException(Exception, "Syntax error in format string at " & $i)