Add sets.keepItIf

stew/shims/sets.nim

@@ -1,4 +1,4 @@
-import std/sets, ../objects
+import std/sets, ../objects, ../templateutils
 
 when not declared(initHashSet):
   template initHashSet*[T](initialSize = 64): auto =
@@ -18,5 +18,16 @@ template init*[T](_: type set[T]): auto =
   var x: set[T]
   x
 
-export sets, objects
+template keepItIf*[T](setParam: var HashSet[T], itPredicate: untyped) =
+  bind evalTemplateParamOnce
+  evalTemplateParamOnce(setParam, s):
+    var itemsToDelete: seq[T]
 
+    for it {.inject.} in s:
+      if not itPredicate:
+        itemsToDelete.add(it)
+
+    for item in itemsToDelete:
+      s.excl item
+
+export sets, objects

tests/all_tests.nim

@@ -27,6 +27,7 @@ import
   test_ptrops,
   test_sequtils2,
   test_sorted_set,
+  test_sets,
   test_templateutils,
   test_results,
   test_varints,

tests/test_sets.nim

@@ -0,0 +1,33 @@
+import
+  unittest,
+  ../stew/shims/sets
+
+suite "shims/sets":
+  test "keepItIf":
+    var s1 = init HashSet[int]
+    s1.incl 10
+    s1.incl 20
+    s1.incl 30
+
+    s1.keepItIf(it > 15)
+
+    check:
+      s1.len == 2
+      10 notin s1
+      20 in s1
+      30 in s1
+
+    var s2 = init HashSet[string]
+    s2.keepItIf(it.len > 0)
+
+    check s2.len == 0
+
+    s2.incl "test"
+    s2.keepItIf(it.len > 10)
+    check s2.len == 0
+
+    s2.incl "test"
+    s2.keepItIf(it.len > 0)
+    check:
+      s2.len == 1
+      "test" in s2