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Programming-Idioms

  • Pascal
  • Scheme
  • Perl

Idiom #329 Read value in a map

Assign to v the value stored in the map m for the key k.

Explain what happens if there is no entry for k in m.

$v = $m{$k} // 'foobar';

defined-or operator, to assign a default value when the lookup fails
$v = $m{$k};

Returns undef when the hash lookup fails
fgl
Type
  TMap = specialize TFPGMap<TKey, TData>;

var
  m: TMap;

...
  if not m.TryGetData(k,v) then ;

if there is no key k, then TryGetData will return False and the content of v will be undefined (in most cases it's memory will be filled with zero's)
var v = m[k];

If no entry, throw an exception; use TryGetValue or GetValueOrDefault instead.
New implementation...
< > ⌨
programming-idioms.org 
$v = $m{$k} // 'foobar';
$v = $m{$k};
Type
  TMap = specialize TFPGMap<TKey, TData>;

var
  m: TMap;

...
  if not m.TryGetData(k,v) then ;
var v = m[k];
v, ok := m[k]
v := m[k]
v = m.get(k);
v = m.get(k);
m.getOrDefault(k, null);
local v=m[k]
v = m[k]
v = m.get(k)
v = m.get(k, "default value")
v = m[k]