[Development] Rvalue pinning in Qt

Thiago Macieira thiago.macieira at intel.com
Mon Jun 20 17:39:55 CEST 2022

On Monday, 20 June 2022 07:46:57 PDT Giuseppe D'Angelo via Development wrote:
> A fancy name for: "if a function/class is operating on a rvalue, should
> it store a copy of it in order to keep it alive?". Consider

In other words, remove the rvalue reference and store a copy from the const-
lvalue reference overload you already have.

> > std::u16string someLongString = u"...";
> > auto tokenizer = QStringTokenizer(someLongString, u"X");
> For this reason QStringTokenizer moves and stores the input if it's an
> rvalue, but only keeps a reference if it's an lvalue.

This means QStringTokenizer must have a QString member and a QString & member. 
The simplest implementation removes one of them.

> > QString s = getString();
> > auto tok = QStringTokenizer(s, u"x");
> would take a copy (given `s` is a view after [4]), while now it only
> takes a reference.


> Opinions?

My only objection is to calling this by a fancy name, "rvalue pinning". Simply 
call what it is: take all parameters by const-lvalue and never store a 

Thiago Macieira - thiago.macieira (AT) intel.com
  Cloud Software Architect - Intel DCAI Cloud Engineering

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