How can I codegen classes like this in C#?

Question

I have multiple classes in a project that are exactly the same except for the name of the class. Basically, they represent glorified enums loaded at runtime from config files. The classes look like this:

public class ClassName : IEquatable<ClassName> {
    public ClassName(string description) {
        Description = description;
    }

    public override bool Equals(object obj) {
        return obj != null &&
            typeof(ClassName).IsAssignableFrom(obj.GetType()) && 
            Equals((ClassName)obj);
    }

    public bool Equals(ClassName other) {
        return other != null && 
            Description.Equals(other.Description);
    }

    public override int GetHashCode() {
        return Description.GetHashCode();
    }

    public override string ToString() {
        return Description;
    }

    public string Description { get; private set; }
}

I see no reason to copy this file and change the class name multiple times. Surely there's a way I can just list what classes I want and have them automatically created for me. How?

Why wouldn't normal class inheritance work? Then the only thing you would repeat would be the constructor. — David
– David, Commented Jan 6, 2010 at 14:55
I don't want classes of one type like this to be comparable with classes of another type like this. Inheritance can handle GetHashCode, ToString and Description, but not Equals. — Instance Hunter
– Instance Hunter, Commented Jan 6, 2010 at 14:57
I'm not saying this applies specifically to your situation, but, anytime I think "How can I quickly duplicate this X times" it raises a big red flag telling me to reconsider my design. Usually, I try to remove duplication rather than automate it. — Eric King
– Eric King, Commented Jan 6, 2010 at 15:20

Craig Stuntz · Accepted Answer · 2010-01-06 15:02:46Z

12

I'd suggest using T4. A substantial advantage of this over code snippets is that if you change your template then all of your code will be updated to match.

Put this in a file with the extension .tt

<#@ template language="C#" #>
<#@ output extension=".codegen.cs" #>
<#@ assembly name="System.dll" #>
<#@ import namespace="System" #>
// <auto-generated>
// This code was generated by a tool. Any changes made manually will be lost
// the next time this code is regenerated.
// </auto-generated>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyStuff
{
<# foreach (string classname in classes) {#>
    public class <#= classname #> : IEquatable<ClassName> 
    {
            public <#= classname #>(string description) {
        Description = description;
    }

    public override bool Equals(object obj) {
        return obj != null &&
            typeof(<#= classname #>).IsAssignableFrom(obj.GetType()) && 
            Equals((<#= classname #>)obj);
    }

    public bool Equals(<#= classname #>other) {
        return other != null && 
            Description.Equals(other.Description);
    }

    public override int GetHashCode() {
        return Description.GetHashCode();
    }

    public override string ToString() {
        return Description;
    }

    public string Description { get; private set; }
    }
    }

<# } #> 
}

<#+ string[] classes = new string[] {  "Class1",
                                       "Class2" };
#>

VS will generate a source file for you. Just add to the array classes when you need a new class.

edited Jan 6, 2010 at 15:02

answered Jan 6, 2010 at 14:56

Craig Stuntz

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3 Comments

Instance Hunter Over a year ago

Supported in express by any chance?

Tj Kellie Over a year ago

If T4 will get VS to generate the source files for you I'm going to have to stop using my homebrew c# tool to create simple codefiles now! Thx for the example Craig

Craig Stuntz Over a year ago

Daniel, yes, you can do this in Express with some configuration. See this question: stackoverflow.com/questions/786734/…

Arjan Einbu · Accepted Answer · 2010-01-06 15:12:36Z

Could you use inheritance with generics?

public class MyBase<T> : IEquatable<MyBase<T>>
    where T : MyBase
{
    public ClassName(string description) {
        Description = description;
    }

    public override bool Equals(object obj) { ... }

    public bool Equals(T other) {
        return other != null && 
            Description.Equals(other.Description);
    }

    public override int GetHashCode() { ... }

    public override string ToString() { ... }

    public string Description { get; private set; }
}

Then you could inherit like this:

public class ClassName1 : MyBase<ClassName1> { ... }
public class ClassName2 : MyBase<ClassName2> { ... }
public class ClassName3 : MyBase<ClassName3> { ... }

CesarGon · Accepted Answer · 2010-01-06 14:54:39Z

2

Have you considered code snippets?

answered Jan 6, 2010 at 14:54

CesarGon

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Comments

Alan Jackson · Accepted Answer · 2010-01-06 15:00:36Z

1

If the classes really are the exact same, could you just use inheritance? The amount of code is pretty small and it doesn't require any extra pre/post processing.

public class Equatable : IEquatable { ... }

public class ClassName1 : Equatable {}
public class ClassName2 : Equatable {}
public class ClassName3 : Equatable {}
public class ClassName4 : Equatable {}

NOTE: All of the code snippet suggestions seem like they would be a maintenance nightmare down the road if you needed to change something.

answered Jan 6, 2010 at 15:00

Alan Jackson

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Comments

Prashant Cholachagudda · Accepted Answer · 2010-01-06 14:55:41Z

0

I would suggest you to create code snippet yourself, that will be quick and easy.

answered Jan 6, 2010 at 14:55

Prashant Cholachagudda

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