SimpleWritableBuffer (Jython API documentation)
Date: 2020-03-21

org.python.core.buffer

## Class SimpleWritableBuffer

- java.lang.Object
- - org.python.core.buffer.BaseBuffer
  - - org.python.core.buffer.Base1DBuffer
    - - org.python.core.buffer.BaseArrayBuffer
      - - org.python.core.buffer.SimpleBuffer
        - - org.python.core.buffer.SimpleWritableBuffer

- All Implemented Interfaces:
    java.lang.AutoCloseable, BufferProtocol, PyBUF, PyBuffer

      public class SimpleWritableBuffer
      extends SimpleBuffer

  Buffer API over a writable one-dimensional array of one-byte items.

- - ### 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
    `SimpleWritableBuffer(int flags, BufferProtocol obj, byte[] storage)` Provide an instance of `SimpleWritableBuffer`, on the entirety of a byte array, meeting the consumer's expectations as expressed in the `flags` argument, which is checked against the capabilities of the buffer type.
    `SimpleWritableBuffer(int flags, BufferProtocol obj, byte[] storage, int index0, int size)` Provide an instance of `SimpleWritableBuffer`, on a slice of a byte array, meeting the consumer's expectations as expressed in the `flags` argument, which is checked against the capabilities of the buffer type.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `PyBuffer` | `getBufferSlice(int flags, int start, int count)` Equivalent to `PyBuffer.getBufferSlice(int, int, int, int)` with stride 1.
    `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.SimpleBuffer

      `byteIndex, getLen, getPointer, getPointer, toString`

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

      `byteIndex, copyFrom, copyFrom, copyTo, getBuf`

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

      `isContiguous`

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

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

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

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

- - ### Constructor Detail

    - #### SimpleWritableBuffer

          public SimpleWritableBuffer(int flags,
                                      BufferProtocol obj,
                                      byte[] storage,
                                      int index0,
                                      int size)
                               throws PyException,
                                      java.lang.NullPointerException

      Provide an instance of `SimpleWritableBuffer`, on a slice of a byte array, meeting the consumer's expectations as expressed in the `flags` argument, which is checked against the capabilities of the buffer type.
      Parameters:
        `flags` - consumer requirements
        `obj` - exporting object (or `null`)
        `storage` - the array of bytes storing the implementation of the exporting object
        `index0` - offset where the data starts in that array (item[0])
        `size` - the number of bytes occupied
      Throws:
        `PyException` - `BufferError` when expectations do not correspond with the type
        `java.lang.NullPointerException`

    - #### SimpleWritableBuffer

          public SimpleWritableBuffer(int flags,
                                      BufferProtocol obj,
                                      byte[] storage)
                               throws PyException,
                                      java.lang.NullPointerException

      Provide an instance of `SimpleWritableBuffer`, on the entirety of a byte array, meeting the consumer's expectations as expressed in the `flags` argument, which is checked against the capabilities of the buffer type.
      Parameters:
        `flags` - consumer requirements
        `obj` - exporting object (or `null`)
        `storage` - the array of bytes storing the implementation of the exporting object
      Throws:
        `PyException` - `BufferError` when expectations do not correspond with the type
        `java.lang.NullPointerException`

  - ### Method Detail

    - #### isReadonly

          public final boolean isReadonly()

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

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

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

    - #### getBufferSlice

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

      Equivalent to `PyBuffer.getBufferSlice(int, int, int, int)` with stride 1.

      `SimpleWritableBuffer` provides an implementation ensuring the returned slice is writable.

      Specified by:
        `getBufferSlice` in interface `PyBuffer`
      Overrides:
        `getBufferSlice` in class `SimpleBuffer`
      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
      Returns:
        a buffer representing the slice

    - #### 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.

      `SimpleBuffer` provides an implementation for slicing contiguous bytes in one dimension. In that case, x(i) = u(r+i) for i = 0..L-1 where u is the underlying buffer, and r and L are the start and count with which x was created from u. Thus y(k) = u(r+s+km), that is, the composite offset is r+s and the stride is m.

      `SimpleWritableBuffer` provides an implementation ensuring the returned slice is writable.

      Specified by:
        `getBufferSlice` in interface `PyBuffer`
      Overrides:
        `getBufferSlice` in class `SimpleBuffer`
      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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