C ++ weird expressions compiled just fine

Question

Why are the following valid C ++ expressions? This is not lambdas

[]{}(); {}[]{}; 

Can someone explain them to me?

Answer 1

The first is a lambda without a list of parameters and a subsequent call. []{} equivalent to [](){} , so the whole line is equivalent

 [](){}(); 

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The second is a pair of curly braces that enter and then immediately close the area, followed by the unused lambda definition without a list of parameters:

 { // empty scope } []{}; // lambda 

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You can refer to http://en.cppreference.com/w/cpp/language/lambda for lambda definition syntax options.

Answer 2

• This lambda call

   []{}(); 

  he is equivalent

   [](){}(); 

• The second is an empty area followed by a (unused) lambda.

Parens are optional for lambdas without parameters.