Scala default parameters from other parameters

Question

I'm trying to do something like the following, and the compiler is not happy...

def foo(db: Database = ctx.defaultDB)(implicit ctx: Context)

That is, if db isn't specified, use ctx to look up the default. The compiler didn't like this version so I tried this:

def foo(ctx: Context, db: Database = ctx.defaultDB)

Compiler didn't like that either...

Answer 1

There are many limitations on default parameter values.

I suggest overloading:

def foo(db: Database)(implicit ctx: Context) = ...

def foo(implicit ctx: Context): Type = foo(ctx.defaultDB)(ctx)

I'm not sure what the exact requirement is, but my quick testing suggests you have to make the return type on the 2nd overload explicit.