expression, executor, plan: rewrite builtin function substring/substr. #3711
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expression/builtin_string.go
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| if mysql.HasBinaryFlag(argType.Flag) { | ||
| types.SetBinChsClnFlag(bf.tp) | ||
| } | ||
| sig := &builtinSubstringSig{baseStringBuiltinFunc{bf}} | ||
| return sig.setSelf(sig), errors.Trace(c.verifyArgs(args)) | ||
| } | ||
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| type builtinSubstringSig struct { |
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I think It's better to define two signature: substr2Args/ substr3Args
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But is there any difference? If so, I need another shared eval function, and let the evalString function in substr2/substr3 call it?
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The difference is that we needn't check the length of args everytime we call eval
expression/builtin_string.go
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| } | ||
| // The forms without a len argument return a substring from string str starting at position pos. | ||
| // The forms with a len argument return a substring len characters long from string str, starting at position pos. | ||
| // The forms that use FROM are standard SQL syntax. It is also possible to use a negative value for pos. | ||
| // In this case, the beginning of the substring is pos characters from the end of the string, rather than the beginning. | ||
| // A negative value may be used for pos in any of the forms of this function. | ||
| strLen := int64(len(str)) | ||
| if pos < 0 { |
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@hanfei1991
But do I need to extract the following part into a shared method, or just write them separately in substr2/substr3?
If yes, the method may be like builtinSubstring(str string, pos, length int, hasLen bool).
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you can write them separately
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expression/builtin_string.go
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| } | ||
| } else { | ||
| d.SetString(str[pos:]) | ||
| if end := pos + length; end < pos { |
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This is not clear. It is better to write like:
end := pos + length
if end < pos ...
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LGTM |
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