$ perl -c -e'use strict; my %h; $h{foo}'
-e syntax OK

$ perl -c -e'use strict; my %h; $h{map $_, foo}'
Bareword "foo" not allowed while "strict subs" in use at -e line 1.
-e had compilation errors.

$ perl -c -e'use strict; my %h; $h{f(foo)}'
Bareword "foo" not allowed while "strict subs" in use at -e line 1.
-e had compilation errors.

$ perl -c -e'use strict; my %h; $h{foo,bar}'
Bareword "foo" not allowed while "strict subs" in use at -e line 1.
Bareword "bar" not allowed while "strict subs" in use at -e line 1.
-e had compilation errors.