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IDProjectCategoryView StatusLast Update
0000653LDMud 3.5LPC Compiler/Preprocessorpublic2017-09-30 18:49
ReporterGnomi Assigned ToGnomi  
Status resolvedResolutionfixed 
Platformi686OSDebian GNU/LinuxOS Version4.0
Fixed in Version3.5.0 
Summary0000653: lvalue 5: Make explicit lvalues fragile
DescriptionExplicitly created lvalues behave somewhat inconsistent. Sometimes they are automatically derefenced, sometimes not.

   int var = 10;
   mixed lv;

   lv = &var; /* typeof(lv) returns T_NUMBER. */
   lv = ({ &var }); /* typeof(lv[0]) returns T_LVALUE. */

I think when pushing an element which is a protected lvalue onto the stack it has to be dereferenced. The only exception is pushing it as an lvalue on the stack (in the above example typeof(lv) and typeof(lv[0]) should return T_NUMBER, but typeof(&lv) and typeof(&(lv[0])) should return T_LVALUE).

So conceptually lvalues are fragile, to keep them you have to use & everywhere you want to copy them.) This is also for security reasons: It shouldn't be possible to give an object an lvalue and observe the values it gets during its processing, unless the object preserves the lvalues by using &.

That's why also x=fun() and x=&(fun()) have to be distinguished (if the former returns an lvalue it has to be changed to an rvalue).
TagsNo tags attached.


child of 0000546 resolvedGnomi Rework lvalue handling 


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Issue History

Date Modified Username Field Change
2009-06-03 15:11 Gnomi New Issue
2009-06-03 15:11 Gnomi Status new => assigned
2009-06-03 15:11 Gnomi Assigned To => Gnomi
2009-06-03 15:12 Gnomi Relationship added child of 0000546
2017-09-30 18:49 Gnomi Status assigned => resolved
2017-09-30 18:49 Gnomi Resolution open => fixed
2017-09-30 18:49 Gnomi Fixed in Version => 3.5.0