It's quite common nowadays to name a function and the application of the function to its input with the same letter. (Possibly more so in applied areas. Certainly many calculus textbooks do this.)

When did this practice start?

In particular, did any of the old masters like Newton, Leibniz, Euler etc. ever write something like $y=y(x)$?

It's quite common nowadays to name a function and the application of the function to its input with the same letter. (Possibly more so in applied areas. Certainly many calculus textbooks do this.)

When did this practice start?

In particular, did any of the old masters like Newton, Leibniz, Euler etc. ever write something like $y=y(x)$?

Clarification: The question is really about the history of this practice. With whom did it start? I didn't want to discuss merits or demerits of this notation. If you want to provide a non standard interpretation of $y=y(x)$, please also back it up with historical references.