Add sortedBy template to sequtils

lib/pure/collections/sequtils.nim

@@ -26,6 +26,8 @@
 when not defined(nimhygiene):
   {.pragma: dirty.}
 
+import algorithm
+
 proc concat*[T](seqs: varargs[seq[T]]): seq[T] =
   ## Takes several sequences' items and returns them inside a new sequence.
   ##
@@ -415,6 +417,19 @@ template mapIt*(varSeq, op: expr) =
     let it {.inject.} = varSeq[i]
     varSeq[i] = op
 
+template sortedBy*(seq1, op: expr): expr =
+  ## Convenience template around the ``sorted`` proc to reduce typing.
+  ##
+  ## The template injects the ``it`` variable which you can use directly in an
+  ## expression.
+  var result {.gensym.} = sorted(seq1, proc(x, y: type(seq1[0])): int =
+    var it {.inject.} = x
+    let a = op
+    it = y
+    let b = op
+    result = cmp(a, b))
+  result
+
 template newSeqWith*(len: int, init: expr): expr =
   ## creates a new sequence, calling `init` to initialize each value. Example:
   ##