Reference Types
I loved arrays! Give me MORE!
Okay. Are you ready for some new syntax?
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MORE C++ syntax? I'll devour it!
A reference is another name for an existing piece of data. In this code, x and z are two names for the same thing!
int x = 5;
int& z = x;
The & means “reference to”, and we read the second line (outwards from z) as "z is a reference to an int". We're not referring to a particular integer value (e.g., 5), we're referring to a storage location that already exists and can hold an int, specifically, the same location in memory used for x. (We can say that x is z's referent.)
Here's how we would represent this reference in our memory model:
New Diagram Rules
- When a function is called, allocate space for all local variables except references (because the references refers to things that were already allocated).
- When a reference is initialized, write its name next to its referent.
- When a reference is destroyed, cross out its name (the referent and reference might not be destroyed at the same time!)
Creating a reference doesn't take up any memory?!? Awesome!!
In essence, yes. References do not consume any memory that you are allowed to access.
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In practice, behind the scenes, at least some of the time, the system probably does need to use some memory to make references work, but it's an under-the-hood how-C++-works-inside detail.
In a later lesson we'll see how references probably work!
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We won't draw it in our diagram because we can't actually access or interact with that under-the-hood data.
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Logically, a reference is an alias (another name for existing data). That's how we'll model it.
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