Why do some Ruby methods need a bang and others don't to be a destructive method?

For example, array.pop doesn't need a bang to permanently alter the array. Why is this so and what was the reasoning behind developing these certain Ruby methods without this conformity?

Bang methods are most commonly used to distinguish between a dangerous and a safe version of the same method. Here are some example cases that one might want to distinguish with a bang/no-bang combination:

• mutator methods - one version changes the object, the other one returns a copy and leaves the original object unchanged
• when encountering an error, one version throws an exception while the other one only writes an error message to the log or does nothing

However, the convention is to leave the bang off if there is only one version that makes sense. For example, poping an array without actually changing it makes no sense. In this case, it would end up being a different operation: Array#last. A lot of methods change the object they are called on, for example setters. We don't need to write these with a bang either, because it's clear that they change the object.

Lastly, there are a few exceptions to this, where some developers might use a bang method without implementing a bang-less counterpart. In these cases, the bang is simply used as a way to making the method calls stand out visually. For example:

• the method does something dangerous or destructive
• the method does something unexpected
• the method has a significant performance impact