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c++syntax
E. Zacarias
E. Zacarias

Reputation: 647

Weird C++ syntax: type definition before a function call

I was reading NodeJS and V8 source, particulary node_contextify.cc file, and I could not understand the following line:

Context::Scope context_scope(debug_context);

I don't understand what is that Context::Scope before what seems to be a function call. I don't think it is a declaration because it is a function code, together with an if and other calls.

Complete relevant code:

...
    if (debug_context.IsEmpty()) {
        // [... lines removed for brevity ...]
    }
    Context::Scope context_scope(debug_context);
    MaybeLocal<Script> script = Script::Compile(debug_context, script_source);
    if (script.IsEmpty())
        return;  // Exception pending.
    args.GetReturnValue().Set(script.ToLocalChecked()->Run());
}
...

What is the meaning of that Context::Scope?

Further information:

File: node/node_contextify.cc (the line 268 is highlighted).

While I understand it is a basic question about syntax, I don't even know how to call it, so I was not able to find any result in Google, StackOverflow or C++ reference.

The question title is one of my attempts when searching for it.

Upvotes: 1

Views: 484

Answers (2)

LWimsey
LWimsey

Reputation: 6647

Context::Scope context_scope(debug_context);

You are declaring an object context_scope of type Context::Scope and initializing it with debug_context
Context::Scope could be a type defined in a class or struct, for example:

class Context {
public:
    using Scope = int;
    ....
}

or, Context::Scope could be a type defined inside a namespace, such as:

namespace Context {
    using Scope = int;
    ...
}

Upvotes: 3

jdigital
jdigital

Reputation: 12276

It's initializing the context_scope variable with debug_context. Context::Scope is the type (here's one ref page http://bespin.cz/~ondras/html/classv8_1_1Context_1_1Scope.html)

Here's another article on using Context::Scope How to correctly use Context::Scope ?

BTW, even if you don't know what to call it, searching for "v8 Context::Scope" will turn up information.

Upvotes: 3

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