[cc-ing laszlo-dev, which is probably more appropriate for this
technical level]
On 17 Nov 2005, at 17:48, Scott Evans wrote:
On Thu, 17 Nov 2005, P T Withington wrote:
The best practice here is to enclose any debug-only computations in
if ($debug) {
...
}
The compiler will omit those statements when you compile without
debugging.
Would be a nice compiler pre-processing step, eh?
The compiler _does_ do simple partial evaluation of constants in if
statements. This was seen as just as good as #ifdef, without having
to invent a new syntax or have a pre-processor.
The compiler automatically defines the constant `$debug` to be true
if you compile your application with --debug, or load it from the
server with ?debug=true and false otherwise. Similarly, it will
define `swfN` as true if you compile with --runtime=swfN or load
with ?lzr=swfN (for N in the supported range, currently 6-8) and
false otherwise.
You can define your own compile-time constants to `lzc` by using `-
D_name_=_value_`, where _value_ should be either `true` or `false`.
By convention, we use `$` as the first character of _name_, but
nothing enforces that.
The compiler will compile only the chosen branch of an if statement
when the condition expression is a compile-time constant (i.e., just
the constant name, no other computation). For example:
if ($slow) {
... slow way ...
} else {
... fast way ...
}
Can be made to run fast by `lzc -D$slow=false`. If you don't supply
a value for $slow at compile time, the compiler will emit both
branches and the if statement will be evaluated at run time. There
is currently no provision for passing compile-time constants through
the server.
Clearly, this mechanism could be abused, making for very unreadable
code, just as is the case with #ifdef. Compile-time constants should
be used judiciously.
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