Do not pass an array as a single pointer

Reason

(pointer, size)-style interfaces are error-prone. Also, a plain pointer (to array) must rely on some convention to allow the callee to determine the size.

Example

Consider:

void copy_n(const T* p, T* q, int n); // copy from [p:p+n) to [q:q+n)

What if there are fewer than n elements in the array pointed to by q? Then, we overwrite some probably unrelated memory. What if there are fewer than n elements in the array pointed to by p? Then, we read some probably unrelated memory. Either is undefined behavior and a potentially very nasty bug.

Alternative

Consider using explicit spans:

void copy(span<const T> r, span<T> r2); // copy r to r2

Example, bad

Consider:

void draw(Shape* p, int n);  // poor interface; poor code
Circle arr[10];
// ...
draw(arr, 10);

Passing 10 as the n argument might be a mistake: the most common convention is to assume [0:n) but that is nowhere stated. Worse is that the call of draw() compiled at all: there was an implicit conversion from array to pointer (array decay) and then another implicit conversion from Circle to Shape. There is no way that draw() can safely iterate through that array: it has no way of knowing the size of the elements.

Alternative: Use a support class that ensures that the number of elements is correct and prevents dangerous implicit conversions. For example:

void draw2(span<Circle>);
Circle arr[10];
// ...
draw2(span<Circle>(arr));  // deduce the number of elements
draw2(arr);    // deduce the element type and array size

void draw3(span<Shape>);
draw3(arr);    // error: cannot convert Circle[10] to span<Shape>

This draw2() passes the same amount of information to draw(), but makes the fact that it is supposed to be a range of Circles explicit. See ???.

Exception

Use zstring and czstring to represent C-style, zero-terminated strings. But when doing so, use std::string_view or span<char> from the GSL to prevent range errors.

Enforcement

• (Simple) ((Bounds)) Warn for any expression that would rely on implicit conversion of an array type to a pointer type. Allow exception for zstring/czstring pointer types.
• (Simple) ((Bounds)) Warn for any arithmetic operation on an expression of pointer type that results in a value of pointer type. Allow exception for zstring/czstring pointer types.