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What exactly does wrapping a type in () do exactly and when should I use it? E.g. blah.(*int)
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It's a type assertion. Type assertions are used to extract the value in an interface type as some other type.
The expression blah.(*int) asserts that the type of the value in blah is *int. If the assertion holds, then the value of the expression is the value stored in blah as a *int. If the assertion does not hold, then the expression panics.
A special form of a type assertion can be used in an assignment to test the assertion:
ip, ok := blah.(*int)
If the value in blah is of *int, then the value is stored in ip and ok is set to true. Otherwise, ip is set to the zero value and ok is false.