Abstract over X

Question

Sorry for this english related question but I only came across that expression in the context of IT. What does abstracting over something mean ? For example abstracting over objects or abstracting over classes. Thanks

Answer 1

It means to pull it out for a function as an argument. It makes more sense in functional programming but imagine you have a function that takes an integer and adds five to it you could make that a variable and have a sum function that would work on any two integers.

That case is not so interesting. Now what if you pulled the addition operation up and made it an argument. Now you have a function that takes two arguments and applies calls the third as a function on them. Here you have abstracted the operation out of the function.

Sorry this is such a weak explanation, I will fix it later when I get a chance. It makes sence with a couple of nice examples, I just have to run ATM.

Answer 2

In this context, the word "abstract" comes from the lambda calculus, where it means "to make something a parameter" (a value parameter or a type parameter). The word is used more generally with other kinds of parameters; for example, mechanisms for "generic programming" often include ways of abstracting over classes.

Probably the easiest language in which to abstract over objects and classes is Smalltalk, where everything (including every class) is an object. Smalltalk, like Ruby which is closely based on Smalltalk, has "duck typing", so for example you could "abstract over" any collection class by writing Smalltalk code that uses only methods common to all collection classes. You could abstract over collection objects in a similar way.