Remove ambiguity in construction of prevector #14030

pull Empact wants to merge 1 commits into bitcoin:master from Empact:ambiguous-prevector-constructor changing 1 files +1 −1

Empact commented at 10:00 AM on August 23, 2018: member

The call with this default argument is redundant with prevector(size_type) on line 251.
Remove default argument to prevector constructor to remove ambiguity
The call with this default argument is redundant with prevector(size_type).
497e90c02b
fanquake added the label Refactoring on Aug 23, 2018
Empact renamed this:
~~Remove default argument to prevector constructor to remove ambiguity~~
Remove ambiguity in construction of prevector
on Aug 23, 2018
Empact commented at 10:35 AM on August 23, 2018: member
Note the effective implementation of resize(n) in this case is:
```
        change_capacity(n);
        _size += n;
        fill(item_ptr(0), n);
```
AkioNak approved
AkioNak commented at 10:57 AM on August 23, 2018: contributor

utACK
DrahtBot commented at 11:28 AM on August 23, 2018: member
Note to reviewers: This pull request conflicts with the following ones:
- #14028 (Explicitly initialize prevector _union by Empact)
If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.
in src/prevector.h:255 in 497e90c02b
```
 251 | @@ -252,7 +252,7 @@ class prevector {
 252 |          resize(n);
 253 |      }
 254 |  
 255 | -    explicit prevector(size_type n, const T& val = T()) : _size(0) {
 256 | +    explicit prevector(size_type n, const T& val) : _size(0) {
```
sipa commented at 4:26 PM on August 23, 2018:

The explicit keyword is also redundant for constructions with >1 argument.

Empact commented at 4:49 PM on August 23, 2018:

FYI: looks like this will change post C++11: https://en.cppreference.com/w/cpp/language/explicit https://en.cppreference.com/w/cpp/language/converting_constructor
theuni commented at 6:05 PM on August 23, 2018:

Neat!

It's not really relevant here, but I'll expand on @Empact's comment because it's something I didn't know, maybe others will benefit as well.

Post c++11:

using ScriptType = prevector<28, unsigned char>; ScriptType vec{1, 255}; // always works vec = ScriptType{1, 255}; // always works vec = {1, 255}; // only works if prevector's ctor is not explicit.

caveat: the 3rd example above does not actually work because of prevector's templated iterator ctor, but that's unrelated.
sipa commented at 4:26 PM on August 23, 2018: member

utACK
theuni commented at 6:11 PM on August 23, 2018: member

utACK 497e90c02b96e8739e8faf3d43e41ba1ff0627b7.

For reference, with c++11, std::vector's matching constructor also removed its default argument and dropped the explicit qualifier.
laanwj merged this on Aug 27, 2018
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