Bug 191 – Cannot refer to member variable in default value for method parameter

-- class c { int x = 5; int foo(int a = x) { return a; } } void main() { assert ((new c).foo() == 5); } -- The above code does not compile, producing the error "need 'this' to access member x". Obliging by changing "int a = x" to "int a = this.x" changes the error to "'this' is only allowed in non-static member functions" followed by "this for x needs to be type c not type int". It can be worked around by removing the default value and manually overriding foo with "int foo() { return foo(x); }", but this is a needless annoyance and precisely what default values are there for. It might be worth noting that this is a longstanding bug which bit me for the first time with DMD 0.128: http://www.digitalmars.com/d/archives/digitalmars/D/bugs/4532.html

This isn't a bug, it is the way it is designed to work. The example will work, however, if you add 'const' to the declaration of x.