)]}'
{
  "commit": "95feb99a9d65641ee022ad7fa087be27a3ed4b84",
  "tree": "83104f6fefed6bacf809a087ff21de3beebb498d",
  "parents": [
    "386755b1acede97cbf88a074bd99dc2c54bedada"
  ],
  "author": {
    "name": "Ben Clayton",
    "email": "bclayton@google.com",
    "time": "Mon Nov 30 22:50:25 2020 +0000"
  },
  "committer": {
    "name": "Commit Bot service account",
    "email": "commit-bot@chromium.org",
    "time": "Mon Nov 30 22:50:25 2020 +0000"
  },
  "message": "Add Castable template class\n\nImplements `As\u003cBlah\u003e()` and `Is\u003cBlah\u003e()` automatically.\n\nThere are several benefits to using this over the pattern of hand-rolled `IsBlah()`, `AsBlah()` methods:\n(1) We don\u0027t have to maintain a whole lot of hand written code.\n(2) These allow us to cast from the base type to _any_ derived type in a single cast. The existing hand-rolled methods usually require a couple of intermediary casts to go from the base type to the leaf type.\n(3) The use of a template parameter means these casts can be called from other template logic.\n\nNote: Unlike the hand-rolled `AsBlah()` methods, it is safe to call `As\u003cT\u003e()` even if the type does not derive from `T`. If the object does not derive from `T` then  `As` will simply return `nullptr`. This allows the calling logic to replace the common pattern of:\n\n```\nif (obj.IsBlah()) {\n   auto* b \u003d obj.AsBlah();\n   ...\n}\n```\n\nwith:\n\n```\nif (auto* b \u003d obj.As\u003cBlah\u003e()) {\n   ...\n}\n```\n\nThis halves the number of virtual method calls, and is one line shorter.\n\nChange-Id: I4312e9831d7de6703a97184640864b8050a34177\nReviewed-on: https://dawn-review.googlesource.com/c/tint/+/34260\nReviewed-by: dan sinclair \u003cdsinclair@chromium.org\u003e\nCommit-Queue: Ben Clayton \u003cbclayton@google.com\u003e\n",
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