Update context to have a generic method for getting request data.

[cheikhshift]

Add a generic method GetAs to get request data.

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[Ozoniuss]

I would find adding this method to be very useful, if support for an older Go version (perhaps in a new Gin release) would no longer be required. If passing custom types in the request context, it helps avoiding some of the code duplication incurred by using the ctx.Get() method followed by a type assertion.

To give a concrete example, in this project I am working on it would've helped to avoid having to define a custom function when retrieving context parameters that are of custom type. I could've used this GetAs in the same way I used GetInt. (code for reference)

id := ctx.GetInt("id")
req, ok := common.CtxGetTyped[casheerapi.UpdateEntryRequest](ctx, "req")
if !ok {
	return
}

With that method, I wouldn't have had to define my custom method CtxGetType which does the same as the new GetAs (actually it does more things for the sake of safety, but I could've omitted them because a middleware is validating the type beforehand).

What's the benefit of this method over the non-generic version? The biggest issue with Get is that a failed type assertion causes a run-time panic, which seems to be the same here?

Avoiding the code duplication by doing the type assertions yourself is a good enough benefit IMO. Functions like GetInt, GetBool, GetTime etc. that are already defined for the library do pretty much the same, except they convert the value to an existing type. If we have those, I would argue that this new function would be just as useful.

[appleboy]

I think we don't need the changes from https://github.com/gin-gonic/gin/pull/3633 anymore.