digitalmars.D.learn - Template type deduction question
- data pulverizer (12/12) May 20 2020 I'd like to pass kernel functions using:
- Basile B. (25/37) May 21 2020 The problem is that "K" is a template type parameter [1].
- Basile B. (4/46) May 21 2020 I've found that even with a template constraint the diagnostic is
- data pulverizer (2/19) May 21 2020 Thanks!
I'd like to pass kernel functions using: ``` auto calculateKernelMatrix(K, T)(K!(T) Kernel, Matrix!(T) data) { ... } ``` and call it using `calculateKernelMatrix(myKernel, myData);` but I get a type deduction error and have to call it using `calculateKernelMatrix!(typeof(myKernel), float)(myKernel, myData);` How do I resolve this?
May 20 2020
On Thursday, 21 May 2020 at 04:46:02 UTC, data pulverizer wrote:I'd like to pass kernel functions using: ``` auto calculateKernelMatrix(K, T)(K!(T) Kernel, Matrix!(T) data) { ... } ``` and call it using `calculateKernelMatrix(myKernel, myData);` but I get a type deduction error and have to call it using `calculateKernelMatrix!(typeof(myKernel), float)(myKernel, myData);` How do I resolve this?The problem is that "K" is a template type parameter [1]. When the compiler deduces the parameter that ends up with a symbol, i.e not a type. To permit a symbol to be deduced you can use a template alias parameter[2] instead: --- struct Matrix(T) {} struct Kernel(T) {} void calculateKernelMatrix(alias K, T)(K!T kernel, Matrix!T data) { } void main() { Matrix!float m; Kernel!float k; calculateKernelMatrix(k,m); // OK } --- However I think that there could be an useful error message, as the current one is of no usefulness. Note that maybe that under the hood there's one but the compiler uses a system of gagging when trying uncertain operations, so that other things can be tried, in case of failure. [1] https://dlang.org/spec/template.html#template_type_parameters [2] https://dlang.org/spec/template.html#aliasparameters
May 21 2020
On Thursday, 21 May 2020 at 07:16:11 UTC, Basile B. wrote:On Thursday, 21 May 2020 at 04:46:02 UTC, data pulverizer wrote:I've found that even with a template constraint the diagnostic is sub-optimal, see issue 20851 [1]. [1] https://issues.dlang.org/show_bug.cgi?id=20851I'd like to pass kernel functions using: ``` auto calculateKernelMatrix(K, T)(K!(T) Kernel, Matrix!(T) data) { ... } ``` and call it using `calculateKernelMatrix(myKernel, myData);` but I get a type deduction error and have to call it using `calculateKernelMatrix!(typeof(myKernel), float)(myKernel, myData);` How do I resolve this?The problem is that "K" is a template type parameter [1]. When the compiler deduces the parameter that ends up with a symbol, i.e not a type. To permit a symbol to be deduced you can use a template alias parameter[2] instead: --- struct Matrix(T) {} struct Kernel(T) {} void calculateKernelMatrix(alias K, T)(K!T kernel, Matrix!T data) { } void main() { Matrix!float m; Kernel!float k; calculateKernelMatrix(k,m); // OK } --- However I think that there could be an useful error message, as the current one is of no usefulness. Note that maybe that under the hood there's one but the compiler uses a system of gagging when trying uncertain operations, so that other things can be tried, in case of failure. [1] https://dlang.org/spec/template.html#template_type_parameters [2] https://dlang.org/spec/template.html#aliasparameters
May 21 2020
On Thursday, 21 May 2020 at 07:16:11 UTC, Basile B. wrote:The problem is that "K" is a template type parameter [1]. When the compiler deduces the parameter that ends up with a symbol, i.e not a type. To permit a symbol to be deduced you can use a template alias parameter[2] instead: --- struct Matrix(T) {} struct Kernel(T) {} void calculateKernelMatrix(alias K, T)(K!T kernel, Matrix!T data) { } void main() { Matrix!float m; Kernel!float k; calculateKernelMatrix(k,m); // OK } ---Thanks!
May 21 2020