Given the syntax for a lambda capture here, I surmise that the syntax for a capture by-copy with initializer is as follows

[identifier initializer] () {}

This means that it can take these forms:

string s = "The quick brown fox jumped over the lazy dog. This is a loooooooooooooong string"

[ x=val ] ( ) { }     // (1)

[ x{val} ] ( ) { }    // (2)

Both forms work for a lambda.

I do understand that the common form is with the use of the assignment operator.

In terms of performance, which of the 2 forms is better?