Compiler Error C3489
'var' is required when the default capture mode is by-value
When you specify that the default capture mode for a lambda expression is by-value, you cannot pass a variable by value to the capture clause of that expression.
To correct this error
Do not explicitly pass the variable to the capture clause, or
Do not specify by-value as the default capture mode, or
Specify by-reference as the default capture mode, or
Pass the variable by reference to the capture clause. (This might change the behavior of the lambda expression.)
Examples
The following example generates C3489 variable n appears by value in the capture clause of a lambda expression whose default mode is by-value:
// C3489a.cpp
int main()
{
int n = 5;
[=, n]() { return n; } (); // C3489
}
The following example shows four possible resolutions to C3489:
// C3489b.cpp
int main()
{
int n = 5;
// Possible resolution 1:
// Do not explicitly pass n to the capture clause.
[=]() { return n; } ();
// Possible resolution 2:
// Do not specify by-value as the default capture mode.
[n]() { return n; } ();
// Possible resolution 3:
// Specify by-reference as the default capture mode.
[&, n]() { return n; } ();
// Possible resolution 4:
// Pass n by reference to the capture clause.
[&n]() { return n; } ();
}