Revision as of 17:17, 31 August 2020 (view source) Chunes (talk \| contribs) (Add Factor) ← Older edit		Revision as of 19:41, 21 September 2020 (view source) rosettacode>Pdolezal (Add comment for Rust) Newer edit →
Line 135: int main() { int junk, junkp; / Print an unitialized variable! / printf("junk: %d\n", junk); / Follow a pointer to unitialized memory! / junkp = malloc(sizeof junkp); if (junkp) printf("junkp: %d\n", junkp); return 0; }</lang> Line 252: There is no undefined value in Déjà Vu. Instead, trying to access an undefined variable raises an exception. <lang dejavu>try: bogus catch name-error: !print "There is no :bogus in the current context" return !print "You won't see this."</lang> If you need to declare a local variable, but don't have a value for it yet, there is the standard function <code>undef</code>, which raises an exception when called but is an actual value that can be passed around and assigned to names. Line 1,236: =={{header\|Raku}}== (formerly Perl 6) Raku has "interesting" values of undef, but unlike Perl 5, doesn't actually have a value named <tt>undef</tt>. Instead, several very different meanings of undefinedness are distinguished. First, <tt>Nil</tt> represents the absence of a value. The absence of a value cannot be stored. Instead, an attempt to assign <tt>Nil</tt> to a storage location causes that location to revert to its uninitialized state, however that is defined. <lang perl6>my $x; $x = 42; $x = Nil; say $x.WHAT; # prints Any()</lang> Line 1,351: Done </pre> =={{header\|Rust}}== All variables in Rust must have defined type and value. For the representation of a value which might not be present, the standard library offers wrapper type <code>Option</code>. <code>Option</code> has two variants: <code>Some</code> (holding a value) and <code>None</code> (indicating the absence of any value): <code>Option</code> is a regular <code>enum</code> type and there is nothing special about it, except for its broad usage. Rust supports raw pointers. Pointers are used for interoperability with other languages and for low-level unsafe operations. Safe Rust code can't use pointers as effective use of a pointer (dereferencing it) requires <code>unsafe</code> block. A pointer may have a ''null'' value: <lang Rust>use std::ptr; let p: *const i32 = ptr::null(); assert!(p.is_null());</lang> =={{header\|Scala}}==

Undefined values: Difference between revisions

Undefined values (view source)

Revision as of 19:41, 21 September 2020