go install github.com/antonmedv/expr/exprgen
Fetch methods generates for all struct/map/array/string named types(exception is map types with unnamed not basic key type like map[struct{...}]int).
To generate just call exprgen with pkg paths as arguments:
exprgen pkg1 pkg2 ...
After call, file *pkg_name*_exprgen.go will be created in each packages from arguments.