June 29, 2011 Problem with a convoluted templated struct | ||||
---|---|---|---|---|
| ||||
Hello. I am trying to implement a templated struct containing a data member created by std.variant.Algebraic instantiated with the struct's template parameters. The problem is, I want to template the struct with e.g. arrays (lists, etc.) of its own type. I don't know any way to do this without ugly string mixin code. I'm not sure if I can explain this clearly, so here's some code: import std.variant; struct Node(Types ...) { Algebraic!(Types) value; //other members, etc... } unittest { //this works Node!(string, int) node1; //this is what I want, but I can't do it, since //Node must be templated Node!(Node[], string, int) node1; } //Now, I can get around this with a string mixin: //(just one argument in this example, but it // could be variadic with more complex code) struct Node2(string t) { mixin("private alias " ~ t ~ " Type;"); Algebraic!(Type) value; } unittest { //works, but ugly Node2!("Node2[]") node; } Is there any way to do this without string mixins? (in case this is proposed: I specifically need structs, not classes. I know I could do this with templated derived classes storing an array/list/whatever with parent class type. Thanks for any help. |
June 29, 2011 Re: Problem with a convoluted templated struct | ||||
---|---|---|---|---|
| ||||
Posted in reply to Kiith-Sa | On Wed, 29 Jun 2011 04:06:02 +0200, Kiith-Sa wrote: > Hello. > > I am trying to implement a templated struct containing a data member created by std.variant.Algebraic instantiated with the struct's template parameters. > > The problem is, I want to template the struct with e.g. arrays (lists, etc.) of its own type. I don't know any way to do this without ugly string mixin code. > > I'm not sure if I can explain this clearly, so here's some code: > > > > import std.variant; > > struct Node(Types ...) > { > Algebraic!(Types) value; > > //other members, etc... > } > > unittest > { > //this works > Node!(string, int) node1; > > //this is what I want, but I can't do it, since //Node must be > templated > Node!(Node[], string, int) node1; > } > > > //Now, I can get around this with a string mixin: //(just one argument in this example, but it // could be variadic with more complex code) > > > struct Node2(string t) > { > mixin("private alias " ~ t ~ " Type;"); Algebraic!(Type) value; > } > > unittest > { > //works, but ugly > Node2!("Node2[]") node; That works because the name Node2 represents the complete type of the templated struct in the struct definition. > } > > > > Is there any way to do this without string mixins? (in case this is proposed: I specifically need structs, not classes. I know I could do this with templated derived classes storing an array/list/whatever with parent class type. > > > Thanks for any help. Providing the container type as an alias template parameter seems to work: import std.container; import std.variant; struct MyAlgebraic(Types ...) {} struct MyList(T) {} struct Node(alias ContainerType, Types ...) { ContainerType!Node container; MyAlgebraic!(Types) value; } unittest { Node!(Array, string, int) node1; Node!(MyList, double, char) node2; } void main() {} But I hit other compilation problems in Algebraic, which I believe to be const-correctness issues. Also consider looking at Phobos ranges. Instead of templatizing on the container type, templatizing on the range type may be better. Ali |
Copyright © 1999-2021 by the D Language Foundation