• Jack (3/3) Feb 25 2021 I started with:
• Paul Backus (3/6) Feb 25 2021 Something like this should work:
• Nathan S. (4/13) Feb 25 2021 `isAssignableNull!(immutable void*)` is true with his definition
• Jack (3/18) Feb 26 2021 yep, it must be true for pointers too. Thank you all guys.
• Nathan S. (13/16) Feb 25 2021 If I understand what you mean by "is assignable to null", this
• Murilo (3/6) Feb 26 2021 You can check if it's null with this `variable is null` and you
• Jack (2/10) Feb 26 2021 I mean a give type T not variablee
• H. S. Teoh (7/19) Feb 26 2021 Why not just:
• Jack (4/22) Feb 28 2021 works too, thanks but I ended up using Nathan S. solution which

Jack <jckj33 gmail.com> writes:

I started with:

enum isAssignableNull(T) = is(T : Object) || isPointer(T);

but how do I cover all cases?

Paul Backus <snarwin gmail.com> writes:

On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:

 enum isAssignableNull(T) = is(T : Object) || isPointer(T);

 but how do I cover all cases?

Something like this should work:

enum isAssignableNull(T) = __traits(compiles, (T t) => t = null);

Nathan S. <no.public.email example.com> writes:

On Friday, 26 February 2021 at 05:34:26 UTC, Paul Backus wrote:
 On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:

 enum isAssignableNull(T) = is(T : Object) || isPointer(T);

 but how do I cover all cases?

 Something like this should work:

 enum isAssignableNull(T) = __traits(compiles, (T t) => t = 
 null);

`isAssignableNull!(immutable void*)` is true with his definition 
but false with yours. Of course you are correct that you cannot 
assign to an immutable pointer.

Jack <jckj33 gmail.com> writes:

On Friday, 26 February 2021 at 05:45:39 UTC, Nathan S. wrote:
 On Friday, 26 February 2021 at 05:34:26 UTC, Paul Backus wrote:
 On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:

 enum isAssignableNull(T) = is(T : Object) || isPointer(T);

 but how do I cover all cases?

 Something like this should work:

 enum isAssignableNull(T) = __traits(compiles, (T t) => t = 
 null);

 `isAssignableNull!(immutable void*)` is true with his 
 definition but false with yours. Of course you are correct that 
 you cannot assign to an immutable pointer.

yep, it must be true for pointers too. Thank you all guys.  
is(typeof(null) : T) works like a charm

Nathan S. <no.public.email example.com> writes:

On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:

 enum isAssignableNull(T) = is(T : Object) || isPointer(T);

 but how do I cover all cases?

If I understand what you mean by "is assignable to null", this 
should do it:

---
enum bool isAssignableNull(T) = is(typeof(null) : T);

// Tests:

immutable string arrayslice = null;
static assert(isAssignableToNull!(immutable string));

void function(int) funptr = null;
static assert(isAssignableToNull!(typeof(funptr)));

int[int] aa = null;
static assert(isAssignableToNull!(int[int]));
---

Murilo <murilomiranda92 hotmail.com> writes:

On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:

 enum isAssignableNull(T) = is(T : Object) || isPointer(T);

 but how do I cover all cases?

You can check if it's null with this `variable is null` and you
can test it with assert as in `assert(variable is null);`

Jack <jckj33 gmail.com> writes:

On Friday, 26 February 2021 at 23:37:18 UTC, Murilo wrote:
 On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:

 enum isAssignableNull(T) = is(T : Object) || isPointer(T);

 but how do I cover all cases?

 You can check if it's null with this `variable is null` and you
 can test it with assert as in `assert(variable is null);`

I mean a give type T not variablee

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Sat, Feb 27, 2021 at 01:03:56AM +0000, Jack via Digitalmars-d-learn wrote:
 On Friday, 26 February 2021 at 23:37:18 UTC, Murilo wrote:
 On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:
 
 enum isAssignableNull(T) = is(T : Object) || isPointer(T);
 
 but how do I cover all cases?

 
 You can check if it's null with this `variable is null` and you
 can test it with assert as in `assert(variable is null);`

 
 I mean a give type T not variablee

Why not just:

	enum isAssignableNull(T) = is(typeof((T t){ t = null; }));

?


T

-- 
What are you when you run out of Monet? Baroque.

Jack <jckj33 gmail.com> writes:

On Saturday, 27 February 2021 at 01:23:06 UTC, H. S. Teoh wrote:
 On Sat, Feb 27, 2021 at 01:03:56AM +0000, Jack via 
 Digitalmars-d-learn wrote:
 On Friday, 26 February 2021 at 23:37:18 UTC, Murilo wrote:
 On Friday, 26 February 2021 at 05:25:14 UTC, Jack wrote:
 I started with:
 
 enum isAssignableNull(T) = is(T : Object) || isPointer(T);
 
 but how do I cover all cases?

 
 You can check if it's null with this `variable is null` and 
 you can test it with assert as in `assert(variable is null);`

 
 I mean a give type T not variablee

 Why not just:

 	enum isAssignableNull(T) = is(typeof((T t){ t = null; }));

 ?


 T

works too, thanks but I ended up using Nathan S. solution which 
is quite fine too:
  enum bool isAssignableNull(T) = is(typeof(null) : T);