Implicit conversion from integral numbers to byte array

[scordio]

I'd like to propose the addition of implicit conversion from integral numbers (byte, short, int, long) to byte array. The concrete use case is code dealing with bitwise operations, mostly related to cryptography.

My wish is to write something like this:

  @ParameterizedTest
  @ValueSource(ints = {Integer.MIN_VALUE, 0, 0xFF, 0xFFFF, 0xFFFFFF, Integer.MAX_VALUE})
  void test(byte[] byteArray) {
    assertThat(byteArray).hasSize(4);
  }

where I can leverage binary and hexadecimal literals which are automatically converted to a byte array using a ByteBuffer with Big Endian order.

I put together a small poc with a custom argument converter. If the proposal is accepted, I'm happy to raise a PR about it.

Deliverables

• A new implicit conversion from byte / short / int / long to byte[]

[sbrannen]

For that use case, you wouldn't use an ArgumentConverter since that can only convert a single argument.

Rather, you would use an ArgumentsAggregator to aggregate all arguments into a single array.

[sbrannen]

In addition, I don't see how we could introduce implicit support for that without breaking existing use cases, but perhaps I'm overlooking something.

[scordio]

@sbrannen I meant something different. Probably a more detailed example would've explained it better.

I don't want to aggregate all the arguments in a single array, I want each argument to be converted into a dedicated byte array, with array size depending on the primitive type.

Following my example:

@ValueSource(ints = {Integer.MIN_VALUE, 0, 0xFF, 0xFFFF, 0xFFFFFF, Integer.MAX_VALUE})

each integer would be converted to a separate byte array of size 4, being the size in bytes of the integer type (i.e., Integer.BYTES). In case of byte values, each array would have size 1; shorts would have arrays of size 2, and longs would have arrays of size 8.

The test cases for the custom converter might explain it better than my words 🙂

[scordio]

Written in a style similar to the official docs, this is what I'd like to have:

Source type	Target type	Example
byte / Byte	byte[]	0xF → ByteBuffer.allocate(Byte.BYTES).put((byte) 0xF).array()
short / Short	byte[]	0xFFF → ByteBuffer.allocate(Short.BYTES).putShort((short) 0xFFF).array()
int / Integer	byte[]	0xFFFFFFF → ByteBuffer.allocate(Integer.BYTES).putInt(0xFFFFFFF).array()
long / Long	byte[]	0xFFFFFFFFL → ByteBuffer.allocate(Long.BYTES).putLong(0xFFFFFFFFL).array()

[scordio]

I raised #2711 to help evaluate this feature.