For reasons I haven’t been able to do anything with Mojo for a few months. Today I decided to catch up with what’s new, install the latest Mojo, and make sure my Julia set generator in Mojo for CPU and GPU still ran. ( https://github.com/laranzu/multijulia ) With the new version (0.26.1.0) I could no…

UnsafePointers used to be mutable (parametric actually?) by default; now you’d have to write UnsafePointer[mut=True, T]. It’s different from a mut argument: mut=True says that you can mutate through this pointer.

Yes, it’s the difference between const T *and T const * in C or C++. My point is that as a Python developer coming to Mojo, it’s not a distinction I care about, or even want to know about. In Mojo on the CPU, prefixing a parameter with mut means I can assign to it. I expect the same behaviour for G…

I don’t see an inconsistency in the meaning of such a program when running on CPU vs. GPU. Could you please elaborate?

On the CPU, I can use a List. If I declare the parameter fn julia(pixels: List[UInt32] … then pixels[idx] = rgbgives a “must be mutable” error. Fix is to change the parameter to fn julia(mut pixels: List[UInt32] … Mojo is consistent about this, whether scalar or compound, parameters are read-on…

There are actually a lot of types in Mojo which have that “interior mutability”. This is a consquence of Origins (and mutability with them) actually being first-class types instead of a thing stuck on the side. You can think of mut foo: UnsafePointer[T, MutOrigin[...]] as having the same API contrac…

As a representative of Real Application Programmers, my reaction to the concept of “interior mutability” is, I’m sorry to say, oh $DEITY why would you do that? I’m aware that fine grained access controls are useful as a higher level concept in application design. I should have write access to my ba…

[image] laranzu: C/C++ have the const T * vs T const * distinction, and 99% of the time only the first form is useful. My experience is that C/C++ programmers rarely use T const * even when they could, it’s not a useful distinction to make. I was talking about *const*T, which is a mutable poi…

Owen, you keep answering questions I didn’t ask. I need to rephrase. My question is why I, as a programmer, cannot just write mut in front of a pointer argument to indicate that I want to assign to it. I can write mut pixels: List[Uint32]and later on pixels[idx] = rgb; So I expect that this woul…

mut pixels: UnsafePointer[UInt32] here mut is telling the the variable pixels is mutable not the data pixels is pointing to. If you want the mutable pointer you have to use that i.e MutUnsafePointer[UInt32]. And If you say why we need mut for pointer specially that is because there are some cases …

Make 'mut' keyword work for GPU function parameters

General

sora March 13, 2026, 6:01pm 9

@laranzu, while I disagree with many of the judgments you made about Mojo in this thread, I’d still like to invite you to share your opinion with the team here.

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Make 'mut' keyword work for GPU function parameters

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