Question

I am trying to write a helper in Razor that looks like the following:

@helper DoSomething<T, U>(Expression<Func<T, U>> expr) where T : class

Unfortunately, the parser thinks that <T is the beginning of an HTML element and I end up with a syntax error. Is it possible to create a helper with Razor that is a generic method? If so, what is the syntax?

Answer 1

No, this is not currently possible. You could write a normal HTML helper instead.

public static MvcHtmlString DoSomething<T, U>(
    this HtmlHelper htmlHelper, 
    Expression<Func<T, U>> expr
) where T : class
{
    ...
}

and then:

@(Html.DoSomething<SomeModel, string>(x => x.SomeProperty))

or if you are targeting the model as first generic argument:

public static MvcHtmlString DoSomething<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper, 
    Expression<Func<TModel, TProperty>> expr
) where TModel : class
{
    ...
}

which will allow you to invoke it like this (assuming of course that your view is strongly typed, but that’s a safe assumption because all views should be strongly typed anyways :-)):

@Html.DoSomething(x => x.SomeProperty)