How can I create a range pipeline that applies a function to elements and flattens the results using temporary containers in Range-V3?

Creating Range Pipelines with Temporary Containers in Range-V3

When dealing with a third-party function that operates on elements of a range and returns a vector, a natural question arises: how to create a range pipeline that applies the function to every element and produces a single, flattened range containing all the returned elements?

In previous versions of Range-V3, attempts to create such pipelines using view::transform and view::join would fail due to the inability to create views of temporary containers.

However, a recent commit has addressed this issue by introducing the view::cache1 operator, which allows for the storage of intermediate results in temporary containers. This enables the creation of range pipelines that utilize temporary containers while maintaining their robustness.

To illustrate this functionality, let's consider the example provided:

<code class="cpp">auto rng = src | view::transform(f) | view::cache1 | view::join;</code>

In this pipeline, view::transform applies the function f to each element of src, producing temporary vectors. view::cache1 caches these temporary vectors, allowing subsequent operations such as view::join to consume the flattened elements.

The updated pipeline ensures that the flattened range rng has the following properties:

• rng is an input range, but not a range of a constant type.
• rng is not a forward range or a common range.

This solution demonstrates the versatility of range-v3 and its ability to handle complex range manipulations involving temporary containers.

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