Why need call class_addMethod?

[zixun]

https://github.com/rentzsch/jrswizzle/blob/semver-1.x/JRSwizzle.m#L54

Why need call class_addMethod? can not ensure origMethod is exist ?

[zongmumask]

https://stackoverflow.com/questions/34502215/proper-way-of-method-swizzling-in-objective-c