众所周知c/cpp的parser是上下文相关，边语义边语法。
cpp11之前经典parser笑话A<A<int>> a.
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| template<typename T>
struct Container {};
int main() {
Container<Container<int>> obj;
}
|
看下clang的输出clang++ test-struct.cpp -Xclang -dump-tokens -v
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| clang -cc1 version 17.0.0 (clang-1700.0.13.5) default target arm64-apple-darwin24.6.0
template 'template' [StartOfLine] Loc=<test-struct.cpp:33:1>
less '<' Loc=<test-struct.cpp:33:9>
typename 'typename' Loc=<test-struct.cpp:33:10>
identifier 'T' [LeadingSpace] Loc=<test-struct.cpp:33:19>
greater '>' Loc=<test-struct.cpp:33:20>
struct 'struct' [StartOfLine] Loc=<test-struct.cpp:34:1>
identifier 'Container' [LeadingSpace] Loc=<test-struct.cpp:34:8>
l_brace '{' [LeadingSpace] Loc=<test-struct.cpp:34:18>
r_brace '}' Loc=<test-struct.cpp:34:19>
semi ';' Loc=<test-struct.cpp:34:20>
int 'int' [StartOfLine] Loc=<test-struct.cpp:36:1>
identifier 'main' [LeadingSpace] Loc=<test-struct.cpp:36:5>
l_paren '(' Loc=<test-struct.cpp:36:9>
r_paren ')' Loc=<test-struct.cpp:36:10>
l_brace '{' [LeadingSpace] Loc=<test-struct.cpp:36:12>
identifier 'Container' [StartOfLine] [LeadingSpace] Loc=<test-struct.cpp:37:5>
less '<' Loc=<test-struct.cpp:37:14>
identifier 'Container' Loc=<test-struct.cpp:37:15>
less '<' Loc=<test-struct.cpp:37:24>
int 'int' Loc=<test-struct.cpp:37:25>
greatergreater '>>' Loc=<test-struct.cpp:37:28>
identifier 'obj' [LeadingSpace] Loc=<test-struct.cpp:37:31>
semi ';' Loc=<test-struct.cpp:37:34>
r_brace '}' [StartOfLine] Loc=<test-struct.cpp:38:1>
eof '' Loc=<test-struct.cpp:38:2>
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哦>>是一个整体
在叠加一下，如果是三个>>>会是什么样子
Container<Container<Container<int>>> obj
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| greatergreater '>>' Loc=<test-struct.cpp:37:38>
greater '>' Loc=<test-struct.cpp:37:40>
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所以clang用了贪心策略。
clang里面还会有greatergreatergreater，是cuda的’>>>’
但是明显’>>’在parser里面是不合适的.
clang是在clang/lib/Parse/ParseTemplate.cpp:ParseGreaterThanInTemplateList里处理，
将’>>’拆分为’>’,’>’然后塞回去一个。如果是’>>>’就拆为’>>’,’>’ 然后将’>>’入队列，’>’是peeking。