src: avoid unnecessary string allocations in SPrintF impl · nodejs/node@d744324 · GitHub

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addaleax

authored and

targos

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src: avoid unnecessary string allocations in SPrintF impl

If we can use a `std::string_view` instead of a `std::string`, let's just do that instead. PR-URL: #60052 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>

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2 files changed

+35-12Lines changed: 35 additions & 12 deletions

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  • debug_utils-inl.h
  • debug_utils.h

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‎src/debug_utils-inl.h‎

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+33-12Lines changed: 33 additions & 12 deletions

Original file line number	Diff line number	Diff line change
@@ -11,25 +11,41 @@
11	11
12	12	namespace node {
13	13
	14	+ template <typename T>
	15	+ concept StringViewConvertible = requires(T a) {
	16	+ {
	17	+ a.ToStringView()
	18	+ } -> std::convertible_to<std::string_view>;
	19	+ };
	20	+ template <typename T>
	21	+ concept StringConvertible = requires(T a) {
	22	+ {
	23	+ a.ToString()
	24	+ } -> std::convertible_to<std::string>;
	25	+ };
	26	+
14	27	struct ToStringHelper {
15	28	template <typename T>
16		- static std::string Convert(
17		- const T& value,
18		- std::string(T::* to_string)() const = &T::ToString) {
19		- return (value.*to_string)();
	29	+ requires(StringConvertible<T>) && (!StringViewConvertible<T>)
	30	+ static std::string Convert(const T& value) {
	31	+ return value.ToString();
20	32	}
	33	+ template <typename T>
	34	+ requires StringViewConvertible<T>
	35	+ static std::string_view Convert(const T& value) {
	36	+ return value.ToStringView();
	37	+ }
	38	+
21	39	template <typename T,
22	40	typename test_for_number = typename std::
23	41	enable_if<std::is_arithmetic<T>::value, bool>::type,
24	42	typename dummy = bool>
25	43	static std::string Convert(const T& value) { return std::to_string(value); }
26		- static std::string Convert(const char* value) {
	44	+ static std::string_view Convert(const char* value) {
27	45	return value != nullptr ? value : "(null)";
28	46	}
29	47	static std::string Convert(const std::string& value) { return value; }
30		- static std::string Convert(std::string_view value) {
31		- return std::string(value);
32		- }
	48	+ static std::string_view Convert(std::string_view value) { return value; }
33	49	static std::string Convert(bool value) { return value ? "true" : "false"; }
34	50	template <unsigned BASE_BITS,
35	51	typename T,
@@ -50,18 +66,23 @@ struct ToStringHelper {
50	66	template <unsigned BASE_BITS,
51	67	typename T,
52	68	typename = std::enable_if_t<!std::is_integral_v<T>>>
53		- static std::string BaseConvert(T& value) { // NOLINT(runtime/references)
	69	+ static auto BaseConvert(T&& value) {
54	70	return Convert(std::forward<T>(value));
55	71	}
56	72	};
57	73
58	74	template <typename T>
59		- std::string ToString(const T& value) {
	75	+ auto ToStringOrStringView(const T& value) {
60	76	return ToStringHelper::Convert(value);
61	77	}
62	78
	79	+ template <typename T>
	80	+ std::string ToString(const T& value) {
	81	+ return std::string(ToStringOrStringView(value));
	82	+ }
	83	+
63	84	template <unsigned BASE_BITS, typename T>
64		- std::string ToBaseString(const T& value) {
	85	+ auto ToBaseString(const T& value) {
65	86	return ToStringHelper::BaseConvert<BASE_BITS>(value);
66	87	}
67	88
@@ -106,7 +127,7 @@ std::string COLD_NOINLINE SPrintFImpl( // NOLINT(runtime/string)
106	127	case 'i':
107	128	case 'u':
108	129	case 's':
109		- ret += ToString(arg);
	130	+ ret += ToStringOrStringView(arg);
110	131	break;
111	132	case 'o':
112	133	ret += ToBaseString<3>(arg);

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‎src/debug_utils.h‎

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+2Lines changed: 2 additions & 0 deletions

Original file line number	Diff line number	Diff line change
@@ -26,6 +26,8 @@ class Environment;
26	26
27	27	template <typename T>
28	28	inline std::string ToString(const T& value);
	29	+ template <typename T>
	30	+ inline auto ToStringOrStringView(const T& value);
29	31
30	32	// C++-style variant of sprintf()/fprintf() that:
31	33	// - Returns an std::string

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