remove duplicate code, simplify code #246

Job	Run time
Intra-doc links	1m 22s
Build target wasm32-unknown-unknown	1m 39s
Bitrot check	1m 41s
Book tests	1m 15s
Build target wasm32-wasi	1m 30s
Rustfmt	17s
Test on ubuntu-latest	7m 9s
Test on i686-unknown-linux-gnu	13m 4s
Test on windows-latest	9m 52s
Test on i686-unknown-linux-gnu with beta features	13m 29s
Test on macOS-latest	7m 47s
Test on i686-unknown-linux-gnu with nightly features	14m 50s
Test on ubuntu-latest with beta features	7m 10s
Test on windows-latest with beta features	9m 46s
Test on macOS-latest with beta features	7m 19s
Test on ubuntu-latest with nightly features	8m 8s
Test on windows-latest with nightly features	11m 40s
Test on macOS-latest with nightly features	7m 39s
	2h 5m 37s

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