Compiler Error C2178

'identifier' cannot be declared with 'specifier' specifier

A mutable specifier was used in a declaration, but the specifier is not allowed in this context.

The mutable specifier can be applied only to names of class data members, and cannot be applied to names declared const or static, and cannot be applied to reference members.

Example

The following sample shows how C2178 may occur, and how to fix it.

// C2178.cpp
// compile with: cl /c /W4 C2178.cpp

class S {
    mutable const int i; // C2178
    // To fix, declare either const or mutable, not both.
};

mutable int x = 4; // C2178
// To fix, remove mutable keyword