C# 中的按需编译时代码生成

Question

I am working in C# and I have a task I would solve in C++ using a template class. However, I cannot use C# generics because the types passed in to the template don't inherit from a single base class or implement a common interface.

Right now I'm using T4 to generate separate code for every type I use, but I want this to happen automatically at compile time based on the code I've written, instead of manually maintaining a list in the text template file.

Is there syntax in the Text Template Transformation Toolkit that would, in effect, work the way templates do in C++?

Edit:

Let's say I have this tt file:

    <# string[] typeNameStrings = new string[2] {"Vector2d", "Vector3d"};
       foreach (string s in substitutions) 
       { #>
           public class SumCalculator<#= s #>
           {
               public <#= s #> sum;
               public SumCalculator<#= s #>(<#= s #> a, <#= s #> b)
               {
                   sum = a + b;
               }
           }
    <# } #>

I don't want to maintain the array typeNameStrings and then use the generated classes SumCalculatorVector2d , SumCalculatorVector3d , etc. Instead, I want to get as close to C++ template functionality as possible (ie SumCalculator<WhateverClass> ). How do I do that?

Answer 1

If I understand you correctly, you're talking about C++'s duck typing mechanism, where it relies on the compile time expansion of templates to figure out the actual code to generate for each separate instance of the template class.

C# doesn't have that, the class code is generated once in its generic form -- that's why there's a requirement that objects used in it abide by normal object rules (your common interface/class requirement).

However, C# does have run-time duck typing using the dynamic keyword. For a (small) performance penalty, and (more importantly) loss of compile-time error checking, you can simply declare your object dynamic and call functions and access fields on it as if you were using C++ templates.