Commutator of field operator with arbitrary functions

[eudo]

In QFT, the commutation relation for the field operator $\hat{\phi}$ and conjugate momentum is
$$[\phi(x,t),\pi(y,t)] = i\delta(x-y)$$
Maybe this is obvious, but what would the commutator of $\phi$ or $\pi$ and, say, $e^{i k\cdot x}$ be?

 

[vanhees71]

It's obviously 0, because $\exp(\mathrm{i} k \cdot x)$ is just a number, which commutes with all operators.

 

[eudo]

Of course... Thanks