Adds toSet to create sets from iterables (#16276)

changelog.md

@@ -58,6 +58,8 @@
 - `strscans.scanf` now supports parsing single characters.
 - `strscans.scanTuple` added which uses `strscans.scanf` internally, returning a tuple which can be unpacked for easier usage of `scanf`. 
 
+- Added `setutils.toSet` that can take any iterable and convert it to a built-in set,
+  if the iterable yields a built-in settable type.
 
 - Added `math.isNaN`.
 

lib/std/setutils.nim

@@ -0,0 +1,32 @@
+#
+#
+#           The Nim Compiler
+#        (c) Copyright 2020 Nim Contributors
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This module adds functionality to the built-in `set` type.
+## See also std/packedsets, std/sets
+
+import typetraits
+
+#[
+  type SetElement* = char|byte|bool|int16|uint16|enum|uint8|int8
+    ## The allowed types of a built-in set.
+]#
+
+template toSet*(iter: untyped): untyped =
+  ## Return a built-in set from the elements of iterable `iter`
+  runnableExamples: 
+    assert "helloWorld".toSet == {'W', 'd', 'e', 'h', 'l', 'o', 'r'}
+    assert toSet([10u16, 20, 30]) == {10u16, 20, 30}
+    assert [30u8, 100, 10].toSet == {10u8, 30, 100}
+    assert toSet(@[1321i16, 321, 90]) == {90i16, 321, 1321}
+    assert toSet([false]) == {false}
+    assert toSet(0u8..10) == {0u8..10}
+  var result: set[elementType(iter)]
+  for x in iter:
+    incl(result, x)
+  result

tests/stdlib/tsetutils.nim

@@ -0,0 +1,14 @@
+discard """
+  targets: "c js"
+"""
+import std/setutils
+
+template main =
+  doAssert "abcbb".toSet == {'a', 'b', 'c'}
+  doAssert toSet([10u8, 12, 13]) == {10u8, 12, 13}
+  doAssert toSet(0u16..30) == {0u16..30}
+  type A = distinct char
+  doAssert [A('x')].toSet == {A('x')}
+  
+main()
+static: main()