BDE 3.122.0 Release

Schedule

• The BDE team announces that the BDE 3.122.0 production release was completed on Monday, July 31, 2023.

BDE 3.122.0 Highlights

bsl::string Has resize_and_overwrite Method

The bsl::string class now provides the resize_and_overwrite method – a C++23 feature – that allows one to avoid the wasted effort of zero filling string contents (as is done by the classic resize) when those positions are about to be overwritten.

Consider the function loadFromIstream that adjusts the size of the output string to the new size (by resize) and then deposits data from the input stream to the available space (by read):

void loadFromIstream(bsl::string     *output,
                     bsl::istream&    input,
                     bsl::streamsize  count)
    // Set the value of the specified 'output' string to the next specified
    // 'count' bytes from the specified 'input' stream.  The behavior is
    // undefined unless ...
{
    // Defensive programming checks here...

    output->resize(count);
         // If 'output' is initially empty, we could:
         //     assert(*output == bsl::string(count, '\0'));

    input.read(output->data(), count);
}

Assuming output is initially empty, it consists of count '\0' characters between the return from resize until it is overwritten by the call to read. Creation of that artifact is of no use here and represents wasted work.

Alternatively:

{
    // Defensive programming checks here...

    auto populator = [ &input ](char *dst, size_t srcSize) {
        input.read(dst, srcSize);
        return input.gcount();  // String size set to actual input count.
    };

    output->resize_and_overwrite(count, populator);
          //      ^^^^^^^^^^^^^^
}

Now, the output string is never set to '\0' characters.

bdlf::BindUtil::bind Correctly Handles MovableRef Arguments

BDE 3.122.0 fixes the behavior of bdlf::BindUtil::bind when it is passed MovableRef and rvalue reference arguments. Prior to this release, in C++03, passing a MovableRef to bdlf::BindUtil::bind would result in the bdlf::Bind object storing a pointer to the passed object instead of move-constructing its copy, which would often result in a dangling pointer:

#include <bdlf_bind.h>
#include <bsl_functional.h>
#include <bsl_string.h>

using namespace BloombergLP;

int f(const bsl::string& s)
{
    return s.size();
}

int main()
{
    bsl::function<int()> func;

    {
        bsl::string s("abc");
        func = bdlf::BindUtil::bind(&f, bslmf::MovableRefUtil::move(s));
                                                // binds a pointer in C++03
    }

    return func();
      // Pre-3.122.0': 'func' dereferences a dangling pointer!
      // Now         : 'func' gets a copy, even via *move*, so no problem.
}

In C++11 and later, the bdlf::Bind object would store a copy of the argument, but would not move-construct it, resulting in an unnecessary copy.

As of BDE 3.122.0, this code behaves as expected in all C++ versions: the bdlf::Bind object will store a move-constructed copy of the argument supplied to the call to bdlf::BindUtil::bind.

Other New Features

• The balcl::CommandLine class now has additional printUsage overloads that allow the user to explicity specify the task’s name.

• The bdlb::NullableAllocatedValue class now has small-object optimization.

• The bslstl_inplace component has added tag types bsl::in_place_type_t and bsl::in_place_index_t.

Fixed DRQSs:

Summary
bdlf_bind: confusion with bslmf::MovableRef<T> args
C++20 work: Add aliases to <bslstl_iterator.h>
C++20 work: Add the ‘starts_with’ and the ‘ends_with’ methods to the ‘bslstl::basic_string_view’
Fix issue in bdlde_quotedprintableencoder.t
Benchmark new ‘bdlb::NumericParseUtil:parseDouble’
Provide C++23 bsl::string::resize_and_overwrite
balcl::Commadline optional ‘taskName’ argument for printUsage
Please add a small-object optimization to bdlb::NullableAllocatedValue
bsl::span usage produces warning in Sun compilation
Please validate reference support for Sun Studio 12.6 for c++11 and above.
reduce bde nb test driver compiler warnings for gcc-10
BDE: fix bslstl_string_test failure for CC 5.12.6
BDE: fix bslstl_array failure for CC 5.12.6
reduce bdl nb issues 20230711
reduce bsl nightly build issues 20230711
Add bsl::in_place_type and bsl::in_place_index
bslmf_isnothrowswappable.h gcc warnings on manual builds
reduce bal nb compile issues 20230712
reduce bal nb warnings 20230713
Fix bdlde_charconvertutf16.cpp to use consistent compiler feature for u16string
reduce bal nb warnings 20230714
normalize use of // for testing only on includes in bde
Cycle Removal: ball: Replace FileObserver2 in ball_log.t.cpp
Cycle Removal: bdlb: Remove transparent[hash|equalto] usage example cycle
Cycle Removal: bslmf:bslmf_isnothrowmoveconstructible test use of movableref
Cycle Removal: bslmt: Remove cycles related to bslmt_testutil.t.cpp
Cycle removal: bsls: Remove bsls_stackaddressutil dependency on SystemTime
Cycle Removal: bslstl: bslstl_iterator.t.cpp remove cyclic dependency on bslstl_set
Cycle Removal: bslstl: Remove stringview.t.cpp dependency on bslstl_map
Cycle Removal: bslmt: Remove cycle with bslstl_ostream and osyncstream