Strided1DWritableBuffer (Jython API documentation)
Date: 2017-06-30

org.python.core.buffer

## Class Strided1DWritableBuffer

- java.lang.Object
- - org.python.core.buffer.BaseBuffer
  - - org.python.core.buffer.Base1DBuffer
    - - org.python.core.buffer.BaseArrayBuffer
      - - org.python.core.buffer.Strided1DBuffer
        - - org.python.core.buffer.Strided1DWritableBuffer

- All Implemented Interfaces:
    AutoCloseable, BufferProtocol, PyBUF, PyBuffer

      public class Strided1DWritableBuffer
      extends Strided1DBuffer

  Read-write buffer API over a one-dimensional array of one-byte items, that are evenly-spaced in a storage array. The storage conventions are described in `Strided1DBuffer` of which this is an extension providing write operations and a writable slice.

- - ### Nested Class Summary

    - ### Nested classes/interfaces inherited from interface org.python.core.PyBuffer

      `PyBuffer.Pointer`

  - ### Field Summary

    - ### Fields inherited from interface org.python.core.PyBUF

      `ANY_CONTIGUOUS, AS_ARRAY, C_CONTIGUOUS, CONTIG, CONTIG_RO, CONTIGUITY, F_CONTIGUOUS, FORMAT, FULL, FULL_RO, INDIRECT, IS_C_CONTIGUOUS, IS_F_CONTIGUOUS, MAX_NDIM, NAVIGATION, ND, RECORDS, RECORDS_RO, SIMPLE, STRIDED, STRIDED_RO, STRIDES, WRITABLE`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Strided1DWritableBuffer(int flags, BufferProtocol obj, byte[] storage, int index0, int count, int stride)` Provide an instance of `Strided1DWritableBuffer` on a particular array of bytes specifying a starting index, the number of items in the result, and a byte-indexing stride.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `PyBuffer` | `getBufferSlice(int flags, int start, int count, int stride)` Get a `PyBuffer` that represents a slice of the current one described in terms of a start index, number of items to include in the slice, and the stride in the current buffer.
    `boolean` | `isReadonly()` Determine whether the consumer is entitled to write to the exported storage.

    - ### Methods inherited from class org.python.core.buffer.Strided1DBuffer

      `byteIndex, getPointer, getPointer`

    - ### Methods inherited from class org.python.core.buffer.BaseArrayBuffer

      `byteIndex, copyFrom, copyFrom, copyTo, getBuf`

    - ### Methods inherited from class org.python.core.buffer.Base1DBuffer

      `getLen, isContiguous`

    - ### Methods inherited from class org.python.core.buffer.BaseBuffer

      `byteAt, byteAt, close, copyTo, getBuffer, getBufferAgain, getBufferSlice, getFormat, getItemsize, getNdim, getNIOByteBuffer, getObj, getShape, getStrides, getSuboffsets, hasArray, intAt, intAt, isReleased, release, storeAt, storeAt, toString`

    - ### Methods inherited from class java.lang.Object

      `equals, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### Strided1DWritableBuffer

          public Strided1DWritableBuffer(int flags,
                                         BufferProtocol obj,
                                         byte[] storage,
                                         int index0,
                                         int count,
                                         int stride)
                                  throws ArrayIndexOutOfBoundsException,
                                         NullPointerException,
                                         PyException

      Provide an instance of `Strided1DWritableBuffer` on a particular array of bytes specifying a starting index, the number of items in the result, and a byte-indexing stride. The result of `byteAt(i)` will be equal to `storage[index0+stride*i]` (whatever the sign of `stride>0`), valid for `0<=i<count`.

      The constructed `PyBuffer` meets the consumer's expectations as expressed in the `flags` argument, or an exception will be thrown if these are incompatible with the type (e.g. the consumer does not specify that it understands the strides array). Note that the actual range in the `storage` array, the lowest and highest index, is not explicitly passed, but is implicit in `index0`, `count` and `stride`. The caller is responsible for checking these fall within the array, or the sub-range the caller is allowed to use.

      Parameters:
        `flags` - consumer requirements
        `obj` - exporting object (or `null`)
        `storage` - raw byte array containing exported data
        `index0` - index into storage of item[0]
        `count` - number of items in the slice
        `stride` - byte-index distance from one element to the next in the new PyBuffer
      Throws:
        `NullPointerException` - if `storage` is null
        `ArrayIndexOutOfBoundsException` - if `index0`, `count` and `stride` are inconsistent with `storage.length`
        `PyException` - (BufferError) when expectations do not correspond with the type

  - ### Method Detail

    - #### isReadonly

          public final boolean isReadonly()

      Determine whether the consumer is entitled to write to the exported storage.

      Declared `final` returning `true` in `Strided1DWritableBuffer` to make checks unnecessary.

      Specified by:
        `isReadonly` in interface `PyBUF`
      Overrides:
        `isReadonly` in class `Strided1DBuffer`
      Returns:
        true if writing is not allowed, false if it is.

    - #### getBufferSlice

          public PyBuffer getBufferSlice(int flags,
                                         int start,
                                         int count,
                                         int stride)

      Get a `PyBuffer` that represents a slice of the current one described in terms of a start index, number of items to include in the slice, and the stride in the current buffer. A consumer that obtains a `PyBuffer` with `getBufferSlice` must release it with `PyBuffer.release()` just as if it had been obtained with `PyBuffer.getBuffer(int)`

      Suppose that x(i) denotes the ith element of the current buffer, that is, the byte retrieved by `this.byteAt(i)` or the unit indicated by `this.getPointer(i)`. A request for a slice where `start` = s, `count` = N and `stride` = m, results in a buffer y such that y(k) = x(s+km) where k=0..(N-1). In Python terms, this is the slice x[s : s+(N-1)m+1 : m] (if m>0) or the slice x[s : s+(N-1)m-1 : m] (if m<0). Implementations should check that this range is entirely within the current buffer.

      In a simple buffer backed by a contiguous byte array, the result is a strided PyBuffer on the same storage but where the offset is adjusted by s and the stride is as supplied. If the current buffer is already strided and/or has an item size larger than single bytes, the new `start` index, `count` and `stride` will be translated from the arguments given, through this buffer's stride and item size. The caller always expresses `start` and `strides` in terms of the abstract view of this buffer.

      `Strided1DBuffer` provides an implementation for slicing already-strided bytes in one dimension. In that case, x(i) = u(r+ip) for i = 0..L-1 where u is the underlying buffer, and r, p and L are the start, stride and count with which x was created from u. Thus y(k) = u(r+sp+kmp), that is, the composite `index0` is r+sp and the composite `stride` is mp.

      `Strided1DWritableBuffer` provides an implementation that returns a writable slice.

      Specified by:
        `getBufferSlice` in interface `PyBuffer`
      Overrides:
        `getBufferSlice` in class `Strided1DBuffer`
      Parameters:
        `flags` - specifying features demanded and the navigational capabilities of the consumer
        `start` - index in the current buffer
        `count` - number of items in the required slice
        `stride` - index-distance in the current buffer between consecutive items in the slice
      Returns:
        a buffer representing the slice

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