gtk:expression-watch-evaluate (watch gvalue)

watch -- a gtk:expression-watch instance
gvale -- an initialized g:value instance

Evaluates the watched expression and on success returns the result in gvalue. This is equivalent to calling the gtk:expression-evaluate function with the expression and the object originally used to create watch.

See the gtk:expression-watch-evaluate-value function which returns the value and does not need a g:value instance.