45 lines
2.3 KiB
Rust
45 lines
2.3 KiB
Rust
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Const qualification, from partial to completely promotable.
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bitflags! {
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#[derive(RustcEncodable, RustcDecodable)]
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flags ConstQualif: u8 {
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// Inner mutability (can not be placed behind a reference) or behind
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// &mut in a non-global expression. Can be copied from static memory.
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const MUTABLE_MEM = 1 << 0,
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// Constant value with a type that implements Drop. Can be copied
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// from static memory, similar to MUTABLE_MEM.
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const NEEDS_DROP = 1 << 1,
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// Even if the value can be placed in static memory, copying it from
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// there is more expensive than in-place instantiation, and/or it may
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// be too large. This applies to [T; N] and everything containing it.
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// N.B.: references need to clear this flag to not end up on the stack.
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const PREFER_IN_PLACE = 1 << 2,
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// May use more than 0 bytes of memory, doesn't impact the constness
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// directly, but is not allowed to be borrowed mutably in a constant.
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const NON_ZERO_SIZED = 1 << 3,
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// Actually borrowed, has to always be in static memory. Does not
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// propagate, and requires the expression to behave like a 'static
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// lvalue. The set of expressions with this flag is the minimum
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// that have to be promoted.
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const HAS_STATIC_BORROWS = 1 << 4,
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// Invalid const for miscellaneous reasons (e.g. not implemented).
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const NOT_CONST = 1 << 5,
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// Borrowing the expression won't produce &'static T if any of these
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// bits are set, though the value could be copied from static memory
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// if `NOT_CONST` isn't set.
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const NON_STATIC_BORROWS = ConstQualif::MUTABLE_MEM.bits |
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ConstQualif::NEEDS_DROP.bits |
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ConstQualif::NOT_CONST.bits
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}
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}
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