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List:       cfe-dev
Subject:    [cfe-dev] Proposal: A "Const tool" for clang
From:       Marshall Clow <mclow.lists () gmail ! com>
Date:       2013-02-05 0:55:45
Message-ID: EBCF0474-3FCB-4F7F-BC09-CA3EAEFBA581 () gmail ! com
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This is the first cut of a proposal for a refactoring tool built on clang.
I have tried to break out what I think are the important issues - but this is only a \
first cut.

The entire proposal is at <http://marshall.calepin.co/a-const-tool-for-llvm.html>, \
only because I think it's a lot easier to read with formatting.

Here's the first section:

== Motivation ==
Adapting an existing code base to use `const` can be a daunting, frustrating task. \
Simply adding "const" to a `Foo &` parameter can have repercussions throughout the \
code base, and may involve adding const to an arbitrary number of other parameters \
(of other functions), or, after making changes in several places, finding that you \
have to back all (or most) of your changes out.

Consider the code snippet:

		void ncfunc1 ( std::string &str ) { str.append ( ' ' ); }
		int cfunc1 ( std::string &str ) { return str.length(); }
		
		void function1 ( std::string &one, std::string& two ) {
			if ( cfunc1 ( one ) > 10 )
				ncfunc ( two );
			}

	* Changing the first parameter to function1 to be `const std::string &` also \
requires changing `cfunc1` to take a `const std::string &`

	* You cannot change the second parameter because it gets passed to `ncfunc1`, which \
cannot be modified to take a `const std::string &`, because it calls the non-const \
member function `append` using that object. (and `std::string::append(char)` cannot \
be made const, because it is part of the standard library)

Broadly speaking, there are three places where const can be added to an existing code \
                base:
	* Parameters that are passed by reference or pointer can be passed by const pointer \
                or const reference.
	* object methods can be marked as const
	* Return values that are returned by pointer or reference can be returned by const \
reference or const pointer. This may involve adding an additional function alongside \
the original, differing only in the return value.


Read the whole thing at:  <http://marshall.calepin.co/a-const-tool-for-llvm.html>, \
and send me comments, please - on list or off. If you know of tools that already do \
this, I'd love to know about them, too.

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists@gmail.com>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly \
                moderated down to (-1, Flamebait).
        -- Yu Suzuki


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