Hi,
Why the program can not return different types of data from the conditional operator?

-----
import std.stdio;

auto foo() {

	if (true) {
		return 0;
	} else
		return "true";
}

void main() {

	writeln(foo);
}

On Thursday, 23 April 2015 at 09:48:21 UTC, Dennis Ritchie wrote:
> Hi,
> Why the program can not return different types of data from the conditional operator?
>
> -----
> import std.stdio;
>
> auto foo() {
>
> 	if (true) {
> 		return 0;
> 	} else
> 		return "true";
> }
>
> void main() {
>
> 	writeln(foo);
> }

Because 0 is an int and "true" is a string.
They're totally different types, and in a statically typed language like D, that just wont work.

On Thursday, 23 April 2015 at 09:48:21 UTC, Dennis Ritchie wrote:
> Hi,
> Why the program can not return different types of data from the conditional operator?
>
> -----
> import std.stdio;
>
> auto foo() {
>
> 	if (true) {
> 		return 0;
> 	} else
> 		return "true";
> }
>
> void main() {
>
> 	writeln(foo);
> }

import std.variant, std.stdio;

auto foo()
{
	if (true)
		return Variant(0);
	else
		return Variant("Hello");
}

void main()
{
	foo.writeln;
}

On Thursday, 23 April 2015 at 10:06:45 UTC, John Colvin wrote:
> On Thursday, 23 April 2015 at 09:48:21 UTC, Dennis Ritchie wrote:
>> Hi,
>> Why the program can not return different types of data from the conditional operator?
>>
>> -----
>> import std.stdio;
>>
>> auto foo() {
>>
>> 	if (true) {
>> 		return 0;
>> 	} else
>> 		return "true";
>> }
>>
>> void main() {
>>
>> 	writeln(foo);
>> }
>
> import std.variant, std.stdio;
>
> auto foo()
> {
> 	if (true)
> 		return Variant(0);
> 	else
> 		return Variant("Hello");
> }
>
> void main()
> {
> 	foo.writeln;
> }

If 'true' is known at compile time, it works:

auto foo() {

	static if (true) {
		return 0;
	} else
		return "true";
}

Thank you all.
I did not know before, that this behavior is characteristic of dynamically typed programming languages.

On Thursday, 23 April 2015 at 10:26:09 UTC, rumbu wrote:
> On Thursday, 23 April 2015 at 10:06:45 UTC, John Colvin wrote:
>> On Thursday, 23 April 2015 at 09:48:21 UTC, Dennis Ritchie wrote:
>>> Hi,
>>> Why the program can not return different types of data from the conditional operator?
>>>
>>> -----
>>> import std.stdio;
>>>
>>> auto foo() {
>>>
>>> 	if (true) {
>>> 		return 0;
>>> 	} else
>>> 		return "true";
>>> }
>>>
>>> void main() {
>>>
>>> 	writeln(foo);
>>> }
>>
>> import std.variant, std.stdio;
>>
>> auto foo()
>> {
>> 	if (true)
>> 		return Variant(0);
>> 	else
>> 		return Variant("Hello");
>> }
>>
>> void main()
>> {
>> 	foo.writeln;
>> }
>
> If 'true' is known at compile time, it works:
>
> auto foo() {
>
> 	static if (true) {
> 		return 0;
> 	} else
> 		return "true";
> }

Yes, but

auto foo() {
	static if (true) {
		return 0;
	} else
		this(statment) is [not.parsed];
}

so it's not just working around a problem of returned type inference.