Implicit Evaluation with PHP Archives: Implicit Evaluation
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30 January 2007
PHP as a Lambda Language
PHP is an imperative language which supports object-oriented programming. However, it supports a number of paradigms closer to what you would expect Lisp or Scheme to allow. I’ve discussed parts of this before, but its time to put together a definitive primer. You’ll learn ways to create entire functions at run time, as well as applying them to entire arrays in a single pass. PHP will seem more LISP-like than it ever has before.
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27 September 2006
Tail Recursion in PHP
There are two types of recursion in the world: tail recursive and non-tail recursive. Non-tail recursive is the more obvious of the two and is used frequently. For instance, when dealing with any kind of hierarchical data (that which is expressed in a tree data structure) a recursive call is likely used to construct the […]
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23 August 2006
Official Introspection, Reflect and Implicit Evaluation PHP.net resources
PHP.net actually provides documentation for each of these topics, but finding it can prove difficult. The following is a collection of the links I’ve discovered.
PHP5 Reflection Classes: These are explicit reflection methods specific to PHP5. I’ve never used them.
Object introspection functions: Introspection functions. There are slight differences in some between PHP4 and PHP5.
Zend Debugger Extensions: […]
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21 August 2006
Variable representation in PHP
In PHP, I like to think each function has its own Dictionary/Hash to manage its scope and that code outside of functions is actually part of a “Main” function. I think of it as a dictionary because through implicit evaluation, you can create variables with spaces and other reasons you’ll see at the conclusion of […]
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1 August 2006
Eval Preformance
I’ve always assumed implicit evaluation was faster than eval, but today, I finally tested that. Eval is four times slower than implicit evaluation.
// Eval Sample
$var = 1;
for ($x = 0; $x < 100000; $x++) {
eval (”$w$var=$var++;”);
}
// Implicit Sample
$var = 1;
for ($x = 0; $x < 100000; $x++) {
$strVar = ‘w’ . $var;
$$strVar = $var++;
}
Each sample […]
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6 January 2006
I used eval() today
Just as self-diagnosis is frowned upon in the medical world, I hesitate to say that my use of eval() was approriate. I’ve been working on a library to transcode HTML into another format, and it became neccessary to support PHP in addition to static HTML. I couldn’t dump to the shell and execute the file […]
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2 January 2006
Evaluating Variables in PHP
This article covers traditional PHP evaluation. There is also an article on implicit PHP evaluation (dynamic evaluation without using eval) if you’d prefer.
I normally discuss the more advanced side of evaluation in this column, but while checking the referral logs today, I found a fair number of visitors coming from Google with searchs like “evaluating […]
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2 January 2006
Limitations of Implicit Evaluation
Implicit evaluation is a very useful thing. For the sake of anyone new to it, implicit evaluation basically lets us treat a variable’s value as an identifier.
$fn = “print”;
$fn (”hello, world!”);
$color = “red”;
$$color = “#ff0000″;
echo $red;
In many ways, it is equivelent to having C/C++’s DEFINE directive as a part of the interpretter rather than pre-processor. […]
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6 December 2005
What is Implicit Evaluation
This article covers implicit PHP evaluation. There is also an article on traditional PHP evaluation (dynamic evaluation using eval) if you’d prefer.
Evaluation is a technique, which, simply refers to evaluating code at runtime. Microsoft Excel does this when a formula is entered in a cell. Many programming languages offer this functionality through various avenues: Mozilla-based […]
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30 November 2005
Combining Implicit Evaluation of Objects with Accessing Arrays
It turns out, that while you can preform implicit evaluation of an object, or a variable, or a variable’s associative array members, trying to merge them all has unexpected behavior.
class foo {
var $arr1;
var $arr2;
}
$foo = new foo();
$foo->arr1 = array(5);
$foo->arr2 = array(5);
function accessFirstElement ($object, $property) {
echo $object->$property[0];
}
accessFirstElement ($foo, “arr1″);
In writing this, I would expect PHP to […]