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@ -54,15 +54,27 @@ actually think about it is probably the general *Deref Coercion*: `&T` coerces t
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Casts are a superset of coercions: every coercion can be explicitly invoked via a cast,
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Casts are a superset of coercions: every coercion can be explicitly invoked via a cast,
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but some changes require a cast. These "true casts" are generally regarded as dangerous or
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but some changes require a cast. These "true casts" are generally regarded as dangerous or
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problematic actions. The set of true casts is actually quite small, and once again revolves
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problematic actions. True casts revolves around raw pointers and the primitive numeric
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largely around pointers. However it also introduces the primary mechanism to convert between
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types. Here's an exhaustive list of all the true casts:
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numeric types.
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* rawptr -> rawptr (e.g. `*mut T as *const T` or `*mut T as *mut U`)
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* rawptr -> rawptr (e.g. `*mut T as *const T` or `*mut T as *mut U`)
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* rawptr <-> usize (e.g. `*mut T as usize` or `usize as *mut T`)
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* rawptr <-> usize (e.g. `*mut T as usize` or `usize as *mut T`)
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* primitive -> primitive (e.g. `u32 as u8` or `u8 as u32`)
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* number -> number (e.g. `u32 as i8` or `i16 as f64`)
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* c-like enum -> integer/bool (e.g. `DaysOfWeek as u8`)
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* c-like enum -> integer/bool (e.g. `DaysOfWeek as u32`)
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* `u8` -> `char`
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* `u8` -> `char`
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* something about arrays?
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For number -> number casts, there are quite a few cases to consider:
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* unsigned to bigger unsigned will zero-extend losslessly
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* unsigned to smaller unsigned will truncate via wrapping
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* signed to unsigned will ... TODO rest of this list
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The casts involving rawptrs also allow us to completely bypass type-safety
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by re-interpretting a pointer of T to a pointer of U for arbitrary types, as
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well as interpret integers as addresses. However it is impossible to actually
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*capitalize* on this violation in Safe Rust, because derefencing a raw ptr is
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`unsafe`.
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## Conversion Traits
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## Conversion Traits
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