Re: auto return for some recursive functions in C++11
On Thursday, 15 January 2015 at 00:05:32 UTC, Xinok wrote: I played with it a bit and it seems to deduce a common type from all the return statements, which would be more in the style of D anyways (take type deduction for arrays). Yes, this has changed some time ago, the specs are already updated: http://dlang.org/function.html#auto-functions Given that the compiler already uses the common type, maybe it should just disregard recursive uses during inference if there is more than one return.
Re: auto return for some recursive functions in C++11
On Wed, 14 Jan 2015 22:29:08 +
bearophile via Digitalmars-d digitalmars-d@puremagic.com wrote:
According to Wikipedia:
http://en.wikipedia.org/wiki/C%2B%2B14#Function_return_type_deduction
C++14 is able to compile code like this:
auto correct(int i) {
if (i == 1)
return i;
else
return correct(i - 1) + i;
}
But not like this:
auto correct(int i) {
if (i != 1)
return correct(i - 1) + i;
else
return i;
}
D isn't able to compile both. Is it a good idea to allow the
first function in D too?
Bye,
bearophile
i'm pretty sure that D *SHOULD* compile the first sample. the spec says
that return type for `auto` function is taken from the first `return`
operator parser met. so for the second `return` the return type is
already known.
i think that this is not just let it compile, but a bug in compiler.
something should be fixed: either compiler or specs.
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Re: auto return for some recursive functions in C++11
On Wednesday, 14 January 2015 at 22:37:22 UTC, ketmar via
Digitalmars-d wrote:
On Wed, 14 Jan 2015 22:29:08 +
bearophile via Digitalmars-d digitalmars-d@puremagic.com
wrote:
According to Wikipedia:
http://en.wikipedia.org/wiki/C%2B%2B14#Function_return_type_deduction
C++14 is able to compile code like this:
auto correct(int i) {
if (i == 1)
return i;
else
return correct(i - 1) + i;
}
But not like this:
auto correct(int i) {
if (i != 1)
return correct(i - 1) + i;
else
return i;
}
D isn't able to compile both. Is it a good idea to allow the
first function in D too?
Bye,
bearophile
i'm pretty sure that D *SHOULD* compile the first sample. the
spec says
that return type for `auto` function is taken from the first
`return`
operator parser met. so for the second `return` the return type
is
already known.
i think that this is not just let it compile, but a bug in
compiler.
something should be fixed: either compiler or specs.
Well, the error the compiler prints is:
Error: forward reference to inferred return type of function call
'correct'
I played with it a bit and it seems to deduce a common type from
all the return statements, which would be more in the style of D
anyways (take type deduction for arrays). For example, the
following code prints float rather than int:
import std.stdio;
auto one(int i)
{
if(i 0)
return cast(int)i;
else
return cast(float)i;
}
void main()
{
writeln(typeid(typeof(one(10;
}
auto return for some recursive functions in C++11
According to Wikipedia:
http://en.wikipedia.org/wiki/C%2B%2B14#Function_return_type_deduction
C++14 is able to compile code like this:
auto correct(int i) {
if (i == 1)
return i;
else
return correct(i - 1) + i;
}
But not like this:
auto correct(int i) {
if (i != 1)
return correct(i - 1) + i;
else
return i;
}
D isn't able to compile both. Is it a good idea to allow the
first function in D too?
Bye,
bearophile
Re: auto return for some recursive functions in C++11
On Wed, 14 Jan 2015 23:07:57 + bearophile via Digitalmars-d digitalmars-d@puremagic.com wrote: ketmar: the spec says that return type for `auto` function is taken from the first `return` operator parser met. so for the second `return` the return type is already known. Do you mean the C++14 spec or the D spec? D spec. i'm not really interested in C++ progress, and certainly not that much that i'll read any of it's specs. The D specs I see are (from: http://dlang.org/function.html ): Auto Functions Auto functions have their return type inferred from any ReturnStatements in the function body. An auto function is declared without a return type. If it does not already have a storage class, use the auto storage class. If there are multiple ReturnStatements, the types of them must be implicitly convertible to a common type. If there are no ReturnStatements, the return type is inferred to be void. i bet that i read somewhere in specs that return type for `auto` function is defined by first `return` parser sees. yet strangely i can't find it right now. maybe that was changed recently, but i'm almost sure that this is not false memory of mine. signature.asc Description: PGP signature
Re: auto return for some recursive functions in C++11
Xinok: I played with it a bit and it seems to deduce a common type from all the return statements, Right, this works according to the D specs (but this is different from the feature I have suggested in the original post). Bye, bearophile
Re: auto return for some recursive functions in C++11
ketmar: the spec says that return type for `auto` function is taken from the first `return` operator parser met. so for the second `return` the return type is already known. Do you mean the C++14 spec or the D spec? The D specs I see are (from: http://dlang.org/function.html ): Auto Functions Auto functions have their return type inferred from any ReturnStatements in the function body. An auto function is declared without a return type. If it does not already have a storage class, use the auto storage class. If there are multiple ReturnStatements, the types of them must be implicitly convertible to a common type. If there are no ReturnStatements, the return type is inferred to be void. Bye, bearophile
Re: auto return for some recursive functions in C++11
On Wednesday, 14 January 2015 at 22:29:09 UTC, bearophile wrote:
According to Wikipedia:
http://en.wikipedia.org/wiki/C%2B%2B14#Function_return_type_deduction
C++14 is able to compile code like this:
auto correct(int i) {
if (i == 1)
return i;
else
return correct(i - 1) + i;
}
...
According to the wiki link:
If multiple return expressions are used in the function's
implementation, then they must all deduce the same type.
So this will NOT work:
auto Correct(int i) {
if (i == 1){
return (int)5;
}else{
return (float)10;
}
}
Error:
prog.cpp: In function 'auto Correct(int)':
prog.cpp:8:19: error: inconsistent deduction for 'auto': 'int'
and then 'float'
return (float)10;
^
So could you please tell me a good use case to for using return
type deduction?
Matheus.
Re: auto return for some recursive functions in C++11
On Thu, 15 Jan 2015 00:05:30 +
Xinok via Digitalmars-d digitalmars-d@puremagic.com wrote:
Well, the error the compiler prints is:
Error: forward reference to inferred return type of function call
'correct'
I played with it a bit and it seems to deduce a common type from
all the return statements, which would be more in the style of D
anyways (take type deduction for arrays). For example, the
following code prints float rather than int:
import std.stdio;
auto one(int i)
{
if(i 0)
return cast(int)i;
else
return cast(float)i;
}
void main()
{
writeln(typeid(typeof(one(10;
}
i remember that there was some discussion about this, but it's all i
can remember about it. ;-)
there were some inconsistencies with deducing return type, AFAIR, but i
don't remember if it leads to some fixes or not. if ony i wasn't so
lazy and take some notes...
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Re: auto return for some recursive functions in C++11
On Thursday, 15 January 2015 at 00:24:09 UTC, Ola Fosheim Grøstad wrote: On Thursday, 15 January 2015 at 00:13:38 UTC, MattCoder wrote: So could you please tell me a good use case to for using return type deduction? Templates. Thanks! - In fact after posting I took a look and found this: http://stackoverflow.com/questions/15737223/when-should-i-use-c14-automatic-return-type-deduction Matheus.
Re: auto return for some recursive functions in C++11
Xinok:
auto one(int i)
{
if(i 0)
return cast(int)i;
else
return cast(float)i;
}
With recent D2 compilers I suggest you to get used to write code
like that like this:
auto one(int i)
{
if(i 0)
return int(i);
else
return float(i);
}
It's better to minimize the usage of cast().
Bye,
bearophile
Re: auto return for some recursive functions in C++11
On Thu, 15 Jan 2015 00:24:07 + via Digitalmars-d digitalmars-d@puremagic.com wrote: On Thursday, 15 January 2015 at 00:13:38 UTC, MattCoder wrote: So could you please tell me a good use case to for using return type deduction? Templates. and returning voldemort types. signature.asc Description: PGP signature
Re: auto return for some recursive functions in C++11
On Thursday, 15 January 2015 at 00:13:38 UTC, MattCoder wrote: So could you please tell me a good use case to for using return type deduction? Templates.
