Why do Objective-C files use the .m extension?

Question

Since I started learning Objective-C and Cocoa, I've been wondering why they have chosen the extension .m for the implementation files - was it supposed to mean something, or was it just a random letter?

I guess this was bothering someone else, so they did a bit of research finding contradicting evidence on the meaning behind .m extension. Ultimately it stands for messages. For the full read: http://pempek.net/blog/2013/11/30/objective-c-file-extension/&utm_medium=email&utm_source=iOS%2BDev%2BWeekly — John Riselvato, Dec 06 '13 at 16:17
`.m` files are implementation files as you said. Knowing Apple likes to prefix everything with `i` it is easy to see that **i**mplementation becomes *mplementation* without said `i`. Then they just used the first letter of mplementation for the file extension: `m`. — Daniel, Oct 25 '19 at 13:57

score 523 · Accepted Answer · edited May 12 '14 at 15:15

523

Today most people would refer to them as "method files", but

"The .m extension originally stood for "messages" when Objective-C was first introduced, referring to a central feature of Objective-C [...]"

(from the book "Learn Objective-C on the Mac" by Mark Dalrymple and Scott Knaster, page 9)

EDIT: To satisfy an itch I emailed Brad Cox, the inventor of Objective-C, about the question and he answered with this single line:

"Because .o and .c were taken. Simple as that."

Here's the email as visual proof:

Visual Proof

edited May 12 '14 at 15:15

nhubbard

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answered Mar 16 '09 at 21:46

splattne

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Brad Cox, RIP. https://en.wikipedia.org/wiki/Brad_Cox – ThomasW Feb 12 '21 at 08:25
What about .oc? Surely it doesn't have to be a single letter, right? – unobatbayar Mar 29 '22 at 00:29
Seems it's also taken. – unobatbayar Mar 29 '22 at 00:34

score 10 · Answer 2 · edited Aug 15 '15 at 03:23

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It stands for "methods". From the comp.lang.objective-C FAQ:

The organisation of Objective-C source is typically similar to that of C or C++ source code, with declarations and object interfaces going into header files named with a .h extension, and definitions and object implementations going in files named with a .m (short for methods) extension.

edited Aug 15 '15 at 03:23

NSDeveloper

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answered Mar 16 '09 at 22:03

Adam Rosenfield

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score 5 · Answer 3 · answered Mar 16 '09 at 21:25

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.m files contain the (m)ethods. Possible reason?

answered Mar 16 '09 at 21:25

baker1990

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m files might contain (m)ultitude of comments as well! go figure:) – NeverStopLearning Jul 17 '14 at 17:56

Why do Objective-C files use the .m extension?

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