Constants are not very constant

[Remixful]

Operating system or device - Godot version:
Windows 10 - v2.1.stable.official on Steam

Issue description (what happened, and what was expected):
I'm not sure if this is intentional or not since I can't find any documentation on it. I'm able to modify the value of constants after they are declared, including the @Gloabl Scope constants. Usually in other languages constants aren't variables and may not be modified.

Steps to reproduce:
Try this in any function that will get called:

print(TYPE_BOOL)
TYPE_BOOL = 999
print(TYPE_BOOL)

Output:

1
999

You can even try declaring your own constants.

[reduz]

heh, I never added a check for that, you must be the first person to find
out.
this will be fun to fix, but I wonder if anyone ever is using it to his/her
advantage

On Sat, Aug 20, 2016 at 6:00 PM, Remixful notifications@github.com wrote:

Operating system or device - Godot version:
Windows 10 - v2.1.stable.official on Steam

Issue description (what happened, and what was expected):
I'm not sure if this is intentional or not since I can't find any
documentation on it. I'm able to modify the value of constants after they
are declared, including the @gloabl Scope
http://docs.godotengine.org/en/latest/classes/class_@global%20scope.html
constants. Usually in other languages constants aren't variables and may
not be modified.

Steps to reproduce:
Try this in any function that will get called:

print(TYPE_BOOL)
TYPE_BOOL = 999
print(TYPE_BOOL)

Output:

1
999

You can even try declaring your own constants.

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[Zylann]

Wow, I thought constants were a compile-time feature? (can they even be?)

[reduz]

I think they are, expressions using them will be reduced properly at
compile time

On Aug 20, 2016 18:09, "Marc" notifications@github.com wrote:

Wow, I thought constants were a compile-time feature? (can they even be?)

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[Zylann]

I mean, if they are processed at compile time, how can they even be modified? Why a check at runtime would even be required? (like writing 1 = 999 is impossible) But I'm not sure if it's technically possible to do that way in GDScript (correct me if I'm wrong)

[manokara]

I think they are indeed processed at compile time, but reduz didn't write a check for an assignment statement involving constants, changing their value. This is probably what's happening:

print(TYPE_BOOL) # reduced to print(1)
TYPE_BOOL = 999 # changes value of constant at compile time
print(TYPE_BOOL) # reduced to print(999)

[akien-mga]

Reopening as the change was reverted.

[reduz]

I will kick to 3.1, since at some point want to add optional typing checks. Those checks will be assignment verifications, so will have the chance to add this code there too (which is also an assignment verification)

[vnen]

Should be solved by #19264.