View source for NMLTutorial/Version check

Version checks in NML are actually pretty straight forward.

NML provides the [http://newgrf-specs.tt-wiki.net/wiki/NML:General#General_variables global variables] <code>openttd_version</code> and <code>ttd_platform</code>. Concerning version checks the built-in [http://newgrf-specs.tt-wiki.net/wiki/NML:Builtin_functions function] <code>version_openttd</code> comes in very handy as it provides an easy means to specify the version instead of manually constructing the version number corresponding to a specific version.

Thus checking for the TTD platform is simply done by an if block:
<pre>
if (ttd_platform != PLATFORM_OPENTTD) {
	error(FATAL, REQUIRES_OPENTTD, string(STR_MIN_OPENTTD_VERSION));
	exit;
}
</pre>

as is the check for a specific OpenTTD (and similarily TTDPatch) version:
<pre>
/* Only define cargo_age_period when that property is available */
if (openttd_version > version_openttd(1, 2, 0, 22713)) {
	item (FEAT_TRAINS, my_engine) {
		property {
			cargo_age_period: 200;
		}
	}
}
</pre>

It's also possible to combine these checks into a single block:
<pre>
/* Long date string codes require OpenTTD > 1.2.0 or r22780 */
if (ttd_platform != PLATFORM_OPENTTD || openttd_version < version_openttd(1, 2, 0, 22780)) {
	error(FATAL, REQUIRES_OPENTTD, string(STR_MIN_OPENTTD_VERSION));
	exit;
}
</pre>