BloombergLP::bslstl::Function_SmallObjectOptimization

Synopsis

Declared in <bslstl_function_smallobjectoptimization.h>

class Function_SmallObjectOptimization;

Types

Name	Description
`InplaceBuffer`	This `union` defines the storage area for a functor representation. The design uses the small-object optimization in an attempt to avoid allocations for objects that are no larger than `InplaceBuffer`. When the target object is no larger than `InplaceBuffer`, the small-object optimization can be used by storing the target directly within the `InplaceBuffer`.
`IsInplaceFunc`	This class is a Boolean metafunction that determines whether or not the specified `FN` template parameter should be allocated within the footprint of the `InplaceBuffer` (i.e., using the small-object optimization.)
`SooFuncSize`	This class template provides a metafunction that `bsl::function` uses to determine the size of an object, and whether to store it using the small-object optimization (SOO) or not. The `value` member of this class encodes the size of the specified `TP` type as follows:

Static Data Members

Name Description

k_NON_SOO_SMALL_SIZE SooFuncSize (below) adds this value to the size of a small stateful functor to indicate that, despite being small, it should not be allocated inplace using the small object optimization (SOO), i.e., because it does not have a nothrow move constructor and cannot, therefore, be swapped safely. When a size larger than this constant is seen, the actual object size can be determined by subtracting this constant. A useful quality of this encoding is that if SZ <= sizeof(InplaceBuffer) for some object size SZ, then SZ + k_NON_SOO_SMALL_SIZE > sizeof(InplaceBuffer), thus SooFuncSize (below) for any object that should not be allocated inplace is larger than sizeof(InplaceBuffer), and the SooFuncSize for any object that should be allocated inplace is smaller than or equal to sizeof(InplaceBuffer), making the test for "is inplace function" simple. Note that it is assumed that no actual object has a size larger than this constant.

Name	Description
`k_NON_SOO_SMALL_SIZE`	`SooFuncSize` (below) adds this value to the size of a small stateful functor to indicate that, despite being small, it should not be allocated inplace using the small object optimization (SOO), i.e., because it does not have a nothrow move constructor and cannot, therefore, be swapped safely. When a size larger than this constant is seen, the actual object size can be determined by subtracting this constant. A useful quality of this encoding is that if `SZ <= sizeof(InplaceBuffer)` for some object size `SZ`, then `SZ + k_NON_SOO_SMALL_SIZE > sizeof(InplaceBuffer)`, thus `SooFuncSize` (below) for any object that should not be allocated inplace is larger than `sizeof(InplaceBuffer)`, and the `SooFuncSize` for any object that should be allocated inplace is smaller than or equal to `sizeof(InplaceBuffer)`, making the test for "is inplace function" simple. Note that it is assumed that no actual object has a size larger than this constant.