add typetraits.pointerBase to return T in ref T|ptr T (#18293)

* add typetraits.deref to return T in ref T|ptr T

* deref => refBase

* refBase=>pointerBase

* [skip ci] address comment

changelog.md

@@ -113,8 +113,12 @@
 
 - Make `{.requiresInit.}` pragma to work for `distinct` types.
 
-- Added a macros `enumLen` for returning the number of items in an enum to the
-  `typetraits.nim` module.
+- `typetraits`:
+  `distinctBase` now is identity instead of error for non distinct types.
+  Added `enumLen` to return the number of elements in an enum.
+  Added `HoleyEnum` for enums with holes, `OrdinalEnum` for enums without holes.
+  Added `hasClosure`.
+  Added `pointerBase` to return `T` for `ref T | ptr T`.
 
 - `prelude` now works with the JavaScript target.
   Added `sequtils` import to `prelude`.
@@ -162,8 +166,6 @@
   Added `symbolName` to return the enum symbol name ignoring the human readable name.
   Added `symbolRank` to return the index in which an enum member is listed in an enum.
 
-- Added `typetraits.HoleyEnum` for enums with holes, `OrdinalEnum` for enums without holes.
-
 - Removed deprecated `iup` module from stdlib, it has already moved to
   [nimble](https://github.com/nim-lang/iup).
 
@@ -293,7 +295,6 @@
 
 - Added `algorithm.merge`.
 
-
 - Added `std/jsfetch` module [Fetch](https://developer.mozilla.org/docs/Web/API/Fetch_API) wrapper for JavaScript target.
 
 - Added `std/jsheaders` module [Headers](https://developer.mozilla.org/en-US/docs/Web/API/Headers) wrapper for JavaScript target.
@@ -322,8 +323,6 @@
 
 - Added `hasDataBuffered` to `asyncnet`.
 
-- Added `hasClosure` to `std/typetraits`.
-
 - Added `std/tempfiles`.
 
 - Added `genasts.genAst` that avoids the problems inherent with `quote do` and can
@@ -345,8 +344,6 @@
 
 - nil dereference is not allowed at compile time. `cast[ptr int](nil)[]` is rejected at compile time.
 
-- `typetraits.distinctBase` now is identity instead of error for non distinct types.
-
 - `os.copyFile` is now 2.5x faster on OSX, by using `copyfile` from `copyfile.h`;
   use `-d:nimLegacyCopyFile` for OSX < 10.5.
 

lib/pure/typetraits.nim

@@ -100,6 +100,16 @@ proc isNamedTuple*(T: typedesc): bool {.magic: "TypeTrait".} =
     doAssert not isNamedTuple((string, int))
     doAssert isNamedTuple(tuple[name: string, age: int])
 
+template pointerBase*[T](_: typedesc[ptr T | ref T]): typedesc =
+  ## Returns `T` for `ref T | ptr T`.
+  runnableExamples:
+    assert (ref int).pointerBase is int
+    type A = ptr seq[float]
+    assert A.pointerBase is seq[float]
+    assert (ref A).pointerBase is A # not seq[float]
+    assert (var s = "abc"; s[0].addr).typeof.pointerBase is char
+  T
+
 proc distinctBase*(T: typedesc): typedesc {.magic: "TypeTrait".} =
   ## Returns the base type for distinct types, or the type itself otherwise.
   ##