Re: Help needed to learn typeof(return)
On Sunday, 27 March 2022 at 01:11:02 UTC, Steven Schveighoffer
wrote:
Not sure what the question here is,
Thanks for the reply. Actually, my problem was this, I forgot the
presence of `LargerOf!(A, B)` template function in that chapter.
When I see it in a function, I thought where is the
implementation of this function ? But later I found it.
And yes, you can get into paradoxical problems like:
```d
auto foo()
{
typeof(return) x;
return x;
}
```
which will not compile.
Yeah, I got the point. In fact, after reading the `Template`
chapter in that book, I am amazed. There are lot of possibilities
in D templates.
Re: Help needed to learn typeof(return)
On 3/26/22 2:25 PM, Vinod K Chandran wrote:
Hi all,
I am reading `Programming in D` online book. There is a paragraph in the
chapter `More Templates`.
```
typeof(return) generates the return type of a function, inside that
function.
For example, instead of defining the calculate() function above as an
auto function, we can be more explicit by replacing auto with
LargerOf!(A, B) in its definition. (Being more explicit would have the
added benefit of obviating at least some part of its function comment.)
```
And it shows this code.
```d
LargerOf!(A, B) calculate(A, B)(A a, B b) {
typeof(return) result; // The type is either A or B
// ...
return result;
}
```
The author says `LargerOf!(A, B)` is used instead of `auto` keyword. How
did compiler understands the return type from `LargerOf!(A, B)`.
Not sure what the question here is, typeof(return) is the type that is
returned from the function.
Where it is useful is if you don't really know what the return type is
(i.e. an auto function) and you need to declare a variable of that type.
In this case, typeof(return) is really `Larger!(A, B)` which is likely
aliased to either A or B.
The equivalent here is:
`LargerOf!(A, B) result;`
But the *spirit* of it is, "I don't want to have to think about whether
it's A or B, just whatever it is, declare a variable of it here".
Hope that helps.
And yes, you can get into paradoxical problems like:
```d
auto foo()
{
typeof(return) x;
return x;
}
```
which will not compile.
-Steve
Re: Help needed to learn typeof(return)
On Saturday, 26 March 2022 at 18:25:54 UTC, Vinod K Chandran wrote: Hi all, The author says `LargerOf!(A, B)` is used instead of `auto` keyword. How did compiler understands the return type from `LargerOf!(A, B)`. Oh Sorry !. I forgot the `LargerOf!(A, B)` definition which is in the same chapter. My fault. Sorry.
Help needed to learn typeof(return)
Hi all,
I am reading `Programming in D` online book. There is a paragraph
in the chapter `More Templates`.
```
typeof(return) generates the return type of a function, inside
that function.
For example, instead of defining the calculate() function above
as an auto function, we can be more explicit by replacing auto
with LargerOf!(A, B) in its definition. (Being more explicit
would have the added benefit of obviating at least some part of
its function comment.)
```
And it shows this code.
```d
LargerOf!(A, B) calculate(A, B)(A a, B b) {
typeof(return) result;// The type is either A or B
// ...
return result;
}
```
The author says `LargerOf!(A, B)` is used instead of `auto`
keyword. How did compiler understands the return type from
`LargerOf!(A, B)`.
