4 ms·

It's not a great practice but super common. I have seen code like $i = "j": $$i = 3; WTF?

mattigames 8y ago
Yeah, I would never hire someone using dynamic variables, any occurrence of "$$" is a no-no and just denotes poor engineering.
- maxxxxx 8y ago
  I think if PHP is the only language you know this pattern probably feels extremely elegant. The JS guys also like to do stuff like this.
  - CzechTech 8y ago
    > The JS guys also like to do stuff like this. Harsh, but fair.
  - mattigames 8y ago
    Just wait until you meet dynamic dynamic variables, nothing more elegant than that... $x=0;$a='x';$b='a'; echo $$$b;
    - duncan-donuts 8y ago
      Haven’t seen that one in the wild. Can that chain just keep going?!
      - _lce0 8y ago
        Not sure how long .. but the chain can be quite long!! $x = 'y'; $y = 'x'; echo $$$$$$$$$$$$$y; I've tested with 1500 `$` and it still works :)
        maxxxxx 8y ago
        Good to know that this method scales well ;).
    - arkh 8y ago
      Lazy coder here : foreach(['a' => closureA, 'b' => closureB, 'c' => closureC] as $name => $toApply) { $myObject->${convertNameToFieldName($name)} = $toApply($something); }
      - Piskvorrr 8y ago
        Too clever by half - a textbook example. This is, in essence, write-only code.
  - 52-6F-62 8y ago
    I write a lot of JS (read: TypeScript if I have any say in it) for work so I’m probably a JS guy. I hate stuff like that. It breaks more than it helps. It overcomplicates trying to dance your way through reasoning what is actually happening. It’s unreliable and I hate it. Carry on...
fiddlerwoaroof 8y ago
This isn't all that uncommon in C. It's not really fundamentally different than pointers to pointers, just a slightly different syntax: int a = 1; int *b = &a; *b = 2; If this can be compiled to efficient assembly, I don't think that kind of variable binding presents much more of a challenge.
- maxxxxx 8y ago
  The content of the $$ is a string so it can be anything including invalid variable names or unknown variables. There is nothing the compiler can do. In C it's totally deterministic.
  - fiddlerwoaroof 8y ago
    This isn't true: a C program could read a pointer address from the user, convert it to an int and store it in the two-star pointer, then dereference it (this is essentially what gdb's `x` command does). All this is essentially a double hashtable lookup (assuming the lexical environment is implemented as a hashtable, but if it's something else, it's similarly trivial): environment[environment["i"]] = 3 People have been compiling extremely dynamic languages since the Lisps, at the very least; and, assembly itself isn't really a "statically typed" language.
    - mikeash 8y ago
      Such a program invokes undefined behavior and thus isn't a correct C program.
      - fiddlerwoaroof 8y ago
        Hmm, as far as I can tell, if you cast an appropriately sized unsigned integer to a pointer type and then dereference the pointer, the result is only UB if the integer isn’t the address of an initialized memory location compatible with the target pointer type.
  - munk-a 8y ago
arkh 8y ago
The fact ${anything interpreted as a string} exists is what makes php great and awful at the same time. It let you do things which will demand a lot of contrived patterns, classes and interfaces in other languages. But it also mean you usually end with some nightmare to maintain full of security holes.

Yeah, I would never hire someone using dynamic variables, any occurrence of "$$" is a no-no and just denotes poor engineering.

maxxxxx 8y ago
I think if PHP is the only language you know this pattern probably feels extremely elegant. The JS guys also like to do stuff like this.
- CzechTech 8y ago
  > The JS guys also like to do stuff like this. Harsh, but fair.
- mattigames 8y ago
  Just wait until you meet dynamic dynamic variables, nothing more elegant than that... $x=0;$a='x';$b='a'; echo $$$b;
  - duncan-donuts 8y ago
    Haven’t seen that one in the wild. Can that chain just keep going?!
    - _lce0 8y ago
      Not sure how long .. but the chain can be quite long!! $x = 'y'; $y = 'x'; echo $$$$$$$$$$$$$y; I've tested with 1500 `$` and it still works :)
      - maxxxxx 8y ago
        Good to know that this method scales well ;).
  - arkh 8y ago
    Lazy coder here : foreach(['a' => closureA, 'b' => closureB, 'c' => closureC] as $name => $toApply) { $myObject->${convertNameToFieldName($name)} = $toApply($something); }
    - Piskvorrr 8y ago
      Too clever by half - a textbook example. This is, in essence, write-only code.
- 52-6F-62 8y ago
  I write a lot of JS (read: TypeScript if I have any say in it) for work so I’m probably a JS guy. I hate stuff like that. It breaks more than it helps. It overcomplicates trying to dance your way through reasoning what is actually happening. It’s unreliable and I hate it. Carry on...

fiddlerwoaroof 8y ago

This isn't all that uncommon in C. It's not really fundamentally different than pointers to pointers, just a slightly different syntax: int a = 1; int *b = &a; *b = 2; If this can be compiled to efficient assembly, I don't think that kind of variable binding presents much more of a challenge.

maxxxxx 8y ago
The content of the $$ is a string so it can be anything including invalid variable names or unknown variables. There is nothing the compiler can do. In C it's totally deterministic.
- fiddlerwoaroof 8y ago
  This isn't true: a C program could read a pointer address from the user, convert it to an int and store it in the two-star pointer, then dereference it (this is essentially what gdb's `x` command does). All this is essentially a double hashtable lookup (assuming the lexical environment is implemented as a hashtable, but if it's something else, it's similarly trivial): environment[environment["i"]] = 3 People have been compiling extremely dynamic languages since the Lisps, at the very least; and, assembly itself isn't really a "statically typed" language.
  - mikeash 8y ago
    Such a program invokes undefined behavior and thus isn't a correct C program.
    - fiddlerwoaroof 8y ago
      Hmm, as far as I can tell, if you cast an appropriately sized unsigned integer to a pointer type and then dereference the pointer, the result is only UB if the integer isn’t the address of an initialized memory location compatible with the target pointer type.
- munk-a 8y ago

arkh 8y ago

The fact ${anything interpreted as a string} exists is what makes php great and awful at the same time. It let you do things which will demand a lot of contrived patterns, classes and interfaces in other languages. But it also mean you usually end with some nightmare to maintain full of security holes.