Make variable type consistent for Rust and C++ #91

Job	Run time
busted (luajit-openresty, ubuntu-latest)	21s
busted (luajit-openresty, windows-latest)	1m 52s
busted (luajit-openresty, macos-latest)	54s
busted (luajit-2.1.0-beta3, ubuntu-latest)	25s
busted (luajit-2.1.0-beta3, windows-latest)	1m 53s
busted (luajit-2.1.0-beta3, macos-latest)	57s
busted (luajit-git, ubuntu-latest)	24s
busted (luajit-git, windows-latest)	1m 44s
busted (luajit-git, macos-latest)	1m 11s
busted (5.4.6, ubuntu-latest)	26s
busted (5.4.6, windows-latest)	1m 27s
busted (5.4.6, macos-latest)	55s
busted (5.1.5, ubuntu-latest)	27s
busted (5.1.5, windows-latest)	1m 28s
busted (5.1.5, macos-latest)	44s
busted (5.3.6, ubuntu-latest)	24s
busted (5.3.6, windows-latest)	1m 51s
busted (5.3.6, macos-latest)	54s
busted (luajit-git, ubuntu-latest, rust)	32s
finish	3s
publish	0s
	18m 52s

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