#Unique ptrs and vectors

21 messages · Page 1 of 1 (latest)

latent ravine
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I understand that I can’t just push back a unique ptr ie. myVec.push_back(uPtr); because it doesn’t support copying but I’d need to use std::move to transfer ownership. Why is it that myVec.push_back(make_unique<…>()); works then? Wouldn’t it just make a copy aswell,. Which wouldn’t work

lusty marlinBOT
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tawdry grail
latent ravine
tawdry grail
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kinda confused at the question. what do you think std::move() does?

latent ravine
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It moves instead of copying

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That’s like all I know lol

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So for like unique ptrs you can’t copy so you can’t directly pass a unique ptr to be pushed on to a vector because it will try to copy it

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But you can std::move the pointer so that ownership is transferred

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So I’m confused on why you can literally pass what is returned by make_unique

dreamy yew
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std::move isn't the only thing that moves

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In general, temporary objects are moved automatically (or more accurately, rvalues are moved automatically, and std::move is just a cast to an rvalue)

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std::move is a kludge that you use when the compiler can't guess that you want to move, which happens when the source isn't an rvalue

latent ravine
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I see

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I guess I’m just confused on an r value now

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What specific is an r value? Because I just know that it evaluates to a value compared to an l value with evaluates to an object

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Also l values can be in place of r values right, so that’s what confuses me in this context

dreamy yew
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Being an rvalue/lvalue is a property of an expression

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Rvalue means that this expression probably refers to a temporary object. Which isn't always true, e.g. std::move can force an rvalue to refer to something else

tawdry grail
dreamy yew