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Linking question
jollytall:
Thanks for the clarification.
Khrys:
The reason why cmem et al. need to be placed at the beginning of the main unit's uses section is a consequence of the way FPC handles unit initialization and involves no magic at all.
The unit tree is traversed left-to-right and depth-first, meaning that in your example...
--- Code: Text [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---u0|+--------------+| |u1 u2|+-------+| |u11 u12
...the order of initialization is as follows: u11, u12, u1, u2, u0
More specifically, the units' initialization blocks are executed in that order. Looking at cmem...
--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---Initialization GetMemoryManager (OldMemoryManager); SetMemoryManager (CmemoryManager);
...you'll see that all it does is replace the RTL's global TMemoryManager record, which GetMem, FreeMem (and class constructors/destructors) all rely on. To make sure that all other units (including their initialize blocks) use the new memory manager, this code needs to run as early as possible - hence the placement at the very beginning in the uses clause of the root unit.
In the case of multiple units defining a function with the same name, it's important to know two things:
FPC allows extensive name shadowing, meaning that the same identifier may refer to different things in different scopes
For example, the objpas unit defines TIntegerArray as a fixed-size array with a total size of 960 MiB (for legacy reasons I assume). If you don't find this useful (I don't), you're free to redefine it as e.g. type TIntegerArray = array of Integer; and the compiler won't complain - it'll simply use the most recently given definition. This also applies to units in the uses clause:
--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---uses u2, u12; foo(); // Refers to u12.foo
--- Code: Pascal [+][-]window.onload = function(){var x1 = document.getElementById("main_content_section"); if (x1) { var x = document.getElementsByClassName("geshi");for (var i = 0; i < x.length; i++) { x[i].style.maxHeight='none'; x[i].style.height = Math.min(x[i].clientHeight+15,306)+'px'; x[i].style.resize = "vertical";}};} ---uses u12, u2; foo(); // Refers to u2.foo
It's of course also possible to explicitly refer to an implementation by prepending the unit name, e.g. u12.foo();
FPC mangles function names in a way that includes the unit name (among other things)
This makes FPC-generated code more powerful in the sense that source-level identifiers don't have to be unique even across objects files / translation units. For example, the Format function in SysUtils is referred to by the symbol SYSUTILS_$$_FORMAT$ANSISTRING$array_of_const$$ANSISTRING by the linker instead of its literal name.
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