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IDProjectCategoryView StatusLast Update
0000906LDMud 3.7Runtimepublic2022-04-28 22:29
ReporterGnomi Assigned To 
Status newResolutionopen 
Platformi686OSDebian GNU/LInuxOS Version5.0
Summary0000906: Revise default-initialization of float variables
DescriptionTLDR: Initialize floats with integer 0 and prevent arithmetic on this value with RTTCs.

Since LDMud 3.2.11 and 3.3.585 floats are default-initialized with 0.0, whereas all other types are initialized with 0. This brings some inconsistent behavior:
  T var;
  if (!var) { write("Uninitialized.\n"); }

For all T (like string, or float|closure) this will print the string, but not for T = float.

The reasons for the change are unknown. This might have been a suggestion for more intuitive behavior in the following cases or just preventing type inconsistencies there:
    float var;

    return (var + 1) / 2
    var += 2;

Previously those expressions would have resulted in 0, 1, 2 as integers, now the result is 0.5, 1.0 and 2.0 as floats.

The change hides an underlying problem with doing arithmetic on the default-zero. In the above example we could initialize var explicitly with 0 and get the old behavior,
thus violating the type restrictions. Also the following code still "works" in LDMud 3.6.5:
    string var;

And results in var being 2.

So in order to remove the default-initialization to 0.0, we need to have a different solution for the arithmetic. Let's start with getting the semantics right.
Do we want to do automatic conversion on assignment:
   string var = 2; // Error or "2"?
   float var = 2; // Error or 2.0?
I would vote 'no', otherwise 'string var = 0;' becomes a tricky case. Also it makes runtime behavior very dependent on the knowledge about the type (so pragma save_types might have a heavy influence) and union types will complicate matters.
Do we want to do automatic conversion on usage:
   float var;
   return (var + 1) / 2; // 0 or 0.5?
Same argument is before: Making runtime behavior dependent on the knowledge of the type seems a bad idea.

Combination of the above questions for +=:
   string var;
   var += 2;

   float var;
   var += 2;
This should have the same meaning as 'var = var + 2;', so it depends on the previous answers.

So in the end I would suggest to:
1. Remove the 0.0 initialization
2. Add RTTC checks to ++, --, +=, -=

But this would break stuff and would only be detectable at runtime...
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Issue History

Date Modified Username Field Change
2022-04-28 22:29 Gnomi New Issue
2022-04-28 22:29 Gnomi Project LDMud => LDMud 3.7