string_view was a proposed feature within the C++ Library Fundamentals TS(N3921) added to C++17
As far as i understand it is a type that represent some kind of string "concept" that is a view of any type of container that could store something viewable as a string.
const std::string& parameter type become string_view ?string_view to take into consideration ?(Educating myself in 2021)
From Microsoft's <string_view>:
The string_view family of template specializations provides an efficient way to pass a read-only, exception-safe, non-owning handle to the character data of any string-like objects with the first element of the sequence at position zero. (...)
From Microsoft's C++ Team Blog std::string_view: The Duct Tape of String Types from August 21st, 2018 (retrieved 2021 Apr 01):
string_view solves the “every platform and library has its own string type” problem for parameters. It can bind to any sequence of characters, so you can just write your function as accepting a string view:
void f(wstring_view); // string_view that uses wchar_t'sand call it without caring what stringlike type the calling code is using (and > for (char*, length) argument pairs just add {} around them) (...)
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Today, the most common “lowest common denominator” used to pass string data around is the null-terminated string (or as the standard calls it, the Null-Terminated Character Type Sequence). This has been with us since long before C++, and provides clean “flat C” interoperability. However, char* and its support library are associated with exploitable code, because length information is an in-band property of the data and susceptible to tampering. Moreover, the null used to delimit the length prohibits embedded nulls and causes one of the most common string operations, asking for the length, to be linear in the length of the string.
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Each programming domain makes up their own new string type, lifetime semantics, and interface, but a lot of text processing code out there doesn’t care about that. Allocating entire copies of the data to process just to make differing string types happy is suboptimal for performance and reliability.