• ixid (49/49) Apr 16 2012 Memoizing a templated version of a function doesn't seem to work,
• bearophile (20/22) Apr 16 2012 A template isn't a function, it's just a recipe to define a
• Andrej Mitrovic (10/12) Apr 16 2012 Instantiate the template first. Either:

"ixid" <nuaccount gmail.com> writes:

Memoizing a templated version of a function doesn't seem to work, 
how would I do it properly? For example:

int test(int n)
{
     return //Do memoizable stuff
}

T test2(T)(T n)
{
     return //Do memoizable stuff
}

void main()
{
     n = memoize!test(n); //is fine
     n = test2(n); //is fine
     n = memoize!test2(n); //gives errors
}


Error	1	Error: template instance ReturnType!(test) 
ReturnType!(test) does not match template declaration 
ReturnType(func...) if (func.length == 1 && 
isCallable!(func))	z:\Dlang\dmd2\src\phobos\std\functional.d	693	
Error	2	Error: ReturnType!(test) is used as a 
type	z:\Dlang\dmd2\src\phobos\std\functional.d	693	
Error	3	Error: template instance ParameterTypeTuple!(test) 
ParameterTypeTuple!(test) does not match template declaration 
ParameterTypeTuple(func...) if (func.length == 1 && 
isCallable!(func))	z:\Dlang\dmd2\src\phobos\std\functional.d	694	
Error	4	Error: ParameterTypeTuple!(test) is used as a 
type	z:\Dlang\dmd2\src\phobos\std\functional.d	693	
Error	5	Error: index is not a type or an 
expression	z:\Dlang\dmd2\src\phobos\std\functional.d	695	
Error	6	Error: template std.typecons.tuple does not match any 
function template 
declaration	z:\Dlang\dmd2\src\phobos\std\functional.d	696	
Error	7	Error: template std.typecons.tuple(T...) cannot deduce 
template function from argument types 
!()(_error_)	z:\Dlang\dmd2\src\phobos\std\typecons.d	687	
Error	8	Error: template main.test does not match any function 
template 
declaration	z:\Dlang\dmd2\src\phobos\std\functional.d	703	
Error	9	Error: template main.test(T) cannot deduce template 
function from argument types !()(_error_)	C:\Documents and 
Settings\Adam.LAPPY\My Documents\Visual Studio 
2008\Projects\d\test2\test2\main.d	5	
Error	10	Error: template instance std.functional.memoize!(test) 
error instantiating	C:\Documents and Settings\Adam.LAPPY\My 
Documents\Visual Studio 2008\Projects\d\test2\test2\main.d	12	
Error	11	Error: forward reference to memoize	C:\Documents and 
Settings\Adam.LAPPY\My Documents\Visual Studio 
2008\Projects\d\test2\test2\main.d	12	

"bearophile" <bearophileHUGS lycos.com> writes:

ixid:

 Memoizing a templated version of a function doesn't seem to 
 work,

A template isn't a function, it's just a recipe to define a 
function given one or more compile-time values or types. So 
memoize works if you instantiate in some way the template:

import std.functional;

int test(int n) {
     return n * n;
}

T test2(T)(T n) {
     return n * n;
}

void main() {
     int n = 5;
     n = memoize!test(n); // OK
     n = test2(n); // OK
     n = memoize!(test2!int)(n); // OK
     n = memoize!(test2!(typeof(n)))(n); // OK
}


Bye,
bearophile

Andrej Mitrovic <andrej.mitrovich gmail.com> writes:

On 4/17/12, ixid <nuaccount gmail.com> wrote:
 Memoizing a templated version of a function doesn't seem to work,
 how would I do it properly?

Instantiate the template first. Either:

n = memoize!(test2!int)(n);

or:

alias test2!int itest;
n = memoize!itest(n);

Actually I'm a little surprised this doesn't work:
memoize!(test2(1));

Seems like IFTI should come into play here but doesn't for some
reason.. anyone else's thoughts?