> why can't we have an optional modern garbage collector built into a systems language?
It's possible in C#. Some language and runtime features like lambdas insist on using the GC, but with some care they can be avoided. The usability becomes worse without these features, but IMO that's not a dramatic downgrade.
Many pieces of the standard library in modern .NET don't require managed heap. Instead, they operate on stuff like Span<byte> which can be backed by anything: unmanaged heap, native stack, or even the memory mapped to user space by a Linux device driver (I did it with DRM, V4L2 and ALSA devices).
It's possible in C#. Some language and runtime features like lambdas insist on using the GC, but with some care they can be avoided. The usability becomes worse without these features, but IMO that's not a dramatic downgrade.
Many pieces of the standard library in modern .NET don't require managed heap. Instead, they operate on stuff like Span<byte> which can be backed by anything: unmanaged heap, native stack, or even the memory mapped to user space by a Linux device driver (I did it with DRM, V4L2 and ALSA devices).