Please help understand the syntax

General Usage
1

In the source code for summarysize.jl

Line 63:
(ss::SummarySize)(@nospecialize obj) = _summarysize(ss, obj)

Line 88 and 89:

(::SummarySize)(obj::Symbol) = 0
(::SummarySize)(obj::SummarySize) = 0

Can someone help explain the syntax used here?

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2

Let’s say you have an instance s of type SummarySize - this function definition makes it so that using s as a function to be called becomes possible (like s(arg)).

(I’ve also moved this thread to “Usage”, since it’s not really a question about how the internals of julia or its design work :slight_smile:)

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3

@Sukera Thank you. Can you point me to the official documentation?

4

These are called “functors” - you’ll find many questions that mention them here on Discourse.

There’s a short section of the docs that demonstrate them here: Methods · The Julia Language

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5

Another name for them in julia is “callable structs”, though I’m not sure there’s a seperate page of documentation available.

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6

@EP-Guy This is really helpful. Thank you so much!