Lazy evaluation of function arguments in C++

Sometimes you’re lazy. You know you need to do something, but don’t want to do it yet. You don’t need to do it right now, only at some later point. And maybe later it turns out that you don’t need to do the entire work, just a part of it or nothing at all! So if you’re eager and do it right now, you might do more work than needed.

The same applies to your code. Sometimes you do things even though it is not necessary. You call a function passing it some arguments that were expensive to calculate and then the function don’t need all of them due to some other arguments. Wouldn’t it be great to only calculate the arguments when they are actually needed?

This is called lazy evaluation of function arguments and this blog post presents how it can be done in C++.

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Author's profile picture Jonathan

Prefer nonmember, nonfriends?

How many member functions does std::string have?

As of C++17 the answer is 153, assuming I counted correctly.

One Hundred Fifty Three.

That is a lot. And as Herb Sutter has pointed out, most of those members could easily be implemented as non-members without loss of performance.

And they should be implemented as nonmembers according to an old guideline from the C++ coding standards: Prefer nonmember, nonfriends. Write free functions whenever possible, not members.

But how true is that advice really?

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Author's profile picture Jonathan

The year is 2017 - Is the preprocessor still needed in C++?

The C++, eh C, preprocessor is wonderful.

Well, no - it isn’t wonderful.

It is a primitive text replacement tool that must be used to work with C++. But is “must” really true? Most of the usage has become obsolete thanks to new and better C++ language features. And many more features like modules will come soon™. So can we get rid of the preprocessor? And if so, how can we do it?

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Author's profile picture Jonathan

cppast - A library to parse and work with the C++ AST

Last year I started standardese, a C++ documentation generator. In order to provide exact documentation, I need to parse C++ code. As I didn’t want to waste time implementing my own parser, which will take ages and don’t work most of the time, I opted to use libclang.

libclang is a C API that exposes the C++ abstract syntax tree (AST) which is built on top of clang. And clang is a good and conforming C++ compiler, so I expected an interface to read the AST that just works and give me the information I need.

Well, I was wrong. Here’s why and how I solved it.

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Author's profile picture Jonathan