[Vm-dev] Re: [Pharo-dev] Should literals be immutable ?

[stepharo]

Levente

I think that the first step is not to make sure that you cannot hack 
inside literals like mad. But to make sure that in
99.99 % of the case, this assumption can hold.

Stef

On 27/10/14 15:46, Levente Uzonyi wrote:
>   
>
>
> On Mon, 27 Oct 2014, Eliot Miranda wrote:
>
>> I disagree.  It's about an incremental improvement.  A per-object 
> immutability bit used to protect against direct alteration of literals 
> works.  Right now there's nothing to stop one recompiling a method, and
> per-object immutability doesn't change that.  So mutable compiled 
> methods are tolerable (at least in VW we kept methods mutable). But 
> having the bit stop direct modification of literals is goodness, not to
> be avoided because it doesn't prevent more exotic modification via 
> become.
>
> But if you allow mutable CompiledMethods, then Clement's example can 
> be rewritten as:
>
> MyClass >> #foo
>
>     ^#(false) first
>         ifFalse: [
>             'first call since compilation' logCr.
>             thisContext method in: [ :method |
>                 (method literalAt: (method literals indexOf: #(false)) 
> put: { true }) ] ]
>         ifTrue: [ 'other calls' logCr ]
>
> (#becomeForward: could also be used on the literal).
>
> How will you avoid implementing the deoptimization of the method (the 
> slow path) when this is possible?
>
> Levente

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