Category Nullptr

Home › All Categories › Nullptr

Nullptr

The name

nullptr is the null pointer. tiko predeclares it as

const nullptr as any ptr = 0

so it is an any ptr whose value is 0. It assigns to, and compares with, every pointer type — typed, zstring ptr, procedure pointers, UDT pointers — with no warning, and if p then treats it as false.

type Node
    nxt as Node ptr
end type

dim as Node ptr head = nullptr
dim as zstring ptr name_ = nullptr
dim as sub( ) callback = nullptr
if head = nullptr then print "empty list"

Why it exists

0 is an integer. Where the target is already a pointer that makes no difference, but where the compiler has to choose a type it chooses integer:

Code	With 0	With nullptr
F( x ), overloads F( integer ) and F( any ptr )	calls F( integer )	calls F( any ptr )
var p = x	p is an integer	p is an any ptr
Echo( x ), function Echo( of T )( byval v as T ) as T	T is integer	T is any ptr

C++11 and C23 added nullptr for the same reason.

Two pointer overloads

nullptr converts to every pointer type equally, so a call that could take it as either of two pointer types is ambiguous, as it is in C++:

sub G overload ( byval a as long ptr )
end sub
sub G overload ( byval a as zstring ptr )
end sub

G( nullptr )                        '' TKO0660, with a note naming the fix
G( cptr( zstring ptr, nullptr ) )   '' the fix

Not a keyword

nullptr is a constant, not a reserved word, for the same reason the fixed-width type names are typedefs: programs may use the name for their own declarations. Whatever a program declares called nullptr — a field, a namespace member, a local, a parameter, a for counter, a module-level variable — replaces tiko's there, with no diagnostic.

0 keeps its meanings alongside it: p = 0 and if p = 0 are legal and silent.

Into an integer

Storing nullptr — or any pointer — into a pointer-sized integer is warning TKO0968:

dim as integer n = nullptr          '' TKO0968: implicit conversion
dim as integer m = cast( integer, nullptr )   '' silent