{"id":4133,"date":"2023-11-05T14:36:49","date_gmt":"2023-11-05T06:36:49","guid":{"rendered":"https:\/\/white-night.club\/?p=4133"},"modified":"2024-02-22T19:29:20","modified_gmt":"2024-02-22T11:29:20","slug":"pg24","status":"publish","type":"post","link":"https:\/\/white-night.club\/index.php\/2023\/11\/05\/pg24\/","title":{"rendered":"MIT6.5830 Lab 2: GoDB Operators\u5b9e\u9a8c\u8bb0\u5f55\uff08\u4e00\uff09"},"content":{"rendered":"\n

\u5b8c\u6210Lab1\u540e\uff0c\u5c31\u8be5\u5f00Lab2\u7684\u65b0\u5751\u4e86\u3002<\/p>\n\n\n\n

<\/div>\n\n\n\n
\n

\u5b9e\u9a8c\u6b65\u9aa4<\/p>\n\u9605\u8bfblab2.md<\/em><\/cite><\/blockquote>\n\n\n\n

\u90a3\u5148\u6765\u770b\u770blab2\u5927\u81f4\u8981\u505a\u4e9b\u4ec0\u4e48\u3002<\/p>\n\n\n\n

<\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
Here's a rough outline of one way you might proceed with your GoDB implementation; more details on the steps in this outline, including exercises, are given in Section 2 below.<\/span><\/span>\n<\/span>\nImplement the operators Filter (filter_op.go) and Join (join_op.go) and verify that their corresponding tests work. The comments in these operators contain details about how they should work.<\/span><\/span>\n<\/span>\nImplement CountAggState, SumAggState, AvgAggState, MinAggState, and MaxAggState in agg_state.go. Here, you will write the logic that actually maintains an aggregation state over a particular field across multiple groups over a running sequence of input tuples. Use integer division for computing the average, since GoDB only supports integers. Only CountAggState, MinAggState, and MaxAggState needs to support both strings and integers, since the other operations do not make sense for strings.<\/span><\/span>\n<\/span>\nImplement the Aggregate (agg_op.go) operator. As with other operators, aggregates implement the Iterator method so that they can be placed in GoDB query plans. Note that the output of an Aggregate operator is an aggregate value of an entire group for each call to the iterator, and that the aggregate constructor takes the aggregation and grouping fields.<\/span><\/span>\n<\/span>\nImplement the Insert (insert_op.go) and Delete (delete_op.go) operators. Like all operators, Insert and Delete implement Iterator, accepting a stream of tuples to insert or delete and outputting a single tuple with an integer field that indicates the number of tuples inserted or deleted. Check that the tests for inserting and deleting tuples work properly.<\/span><\/span>\n<\/span>\nImplement the Project (project_op.go), OrderBy (order_by_op.go), and Limit (limit_op.go) operators.<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    \n
  • \u9996\u5148\u662fFilter\u548cJoin\u4e24\u4e2a\u8fd0\u7b97\u7b26\u3002Join\u5e94\u8be5\u5f88\u719f\u6089\u4e86\uff0c\u5929\u5929LEFT JOIN\u554aINNER JOIN\u7684\u3002\u4f46\u662fFilter\u53ef\u80fd\u6bd4\u8f83\u5c11\u89c1\uff1f\u5177\u4f53\u7684\u8fb9\u505a\u5b9e\u9a8c\u8fb9\u8bb2\u3002<\/li>\n\n\n\n
  • aggregation–\u805a\u5408\u3002\u90a3\u5c31\u662f\u5b9e\u73b0GROUP BY\uff1f<\/li>\n\n\n\n
  • \u5404\u79cd\u805a\u5408\u51fd\u6570\u3002SUM\u554a\uff0cAVG\u554a\uff0cCOUNT\u554a\uff0c\u8fd9\u4e9b\u5e73\u65f6\u4e5f\u5f88\u719f\u6089\u4e86\u3002<\/li>\n\n\n\n
  • crud\u4e2d\u7684c\u548cd\u3002\u589e\u5220\u529f\u80fd\u3002<\/li>\n\n\n\n
  • \u6295\u5f71\uff0c\u6392\u5e8f\u548climit\u3002project\u53ef\u80fd\u4e0d\u592a\u719f\u6089\u4f46\u53e6\u5916\u4e24\u4e2a\u4e5f\u5f88\u719f\u6089\u4e86\u3002<\/li>\n<\/ul>\n\n\n\n
    \u5927\u81f4\u8981\u5b8c\u6210\u7684\u76ee\u6807\u6709\u4e86\u3002\u770b\u8d77\u6765\u5b8c\u6210lab2\u5c31\u80fd\u770b\u5230\u4e00\u4e2a\u6bd4\u8f83\u57fa\u7840\u7684dbms\u4e86\u3002<\/p>\n\n\n\n
    <\/div>\n\n\n\n
    \n
    \u5b9e\u9a8c\u6b65\u9aa4<\/p>\nExercise 1<\/em><\/cite><\/blockquote>\n\n\n\n
    join\u8981\u5b8c\u6210\u7684\u4ee3\u7801\u6bd4\u8f83\u591a\uff0c\u800c\u4e14\u6709\u70b9\u96be\u5ea6\u3002\u90a3\u5148\u6765\u770b\u770bFilter\u3002<\/p>\n\n\n\n
    \u5148\u6765\u770b\u770bFilter\u7684\u7ed3\u6784\u3002T constraints.Ordered\u8868\u793a\u7684\u662f\u201c\u5b9a\u4e49\u4e00\u4e2a\u7c7b\u578bT\uff0c\u8be5\u7c7b\u578b\u6ee1\u8db3constraints.Ordered\u7ea6\u675f\u201d\u3002\u800cconstraints.Ordered\u7ea6\u675f\u6307\u7684\u662f\u201c\u8be5\u7c7b\u578b\u7684\u503c\u5fc5\u987b\u53ef\u4ee5\u8fdb\u884c\u5927\u5c0f\u6bd4\u8f83\u201d\u3002\u6bd4\u5982int\u554a\uff0cstring\uff08\u6309\u5b57\u5178\u5e8f\u6392\u5e8f\uff09\u554a\u8fd9\u4e9b\u3002getter func(DBValue) T\u76f8\u5f53\u4e8e\u4e00\u4e2a\u7c7b\u578b\u8f6c\u6362\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    type<\/span> <\/span>Filter<\/span>[T constraints.Ordered] <\/span>struct<\/span> {<\/span><\/span>\n\top     BoolOp<\/span><\/span>\n\tleft   Expr<\/span><\/span>\n\tright  Expr<\/span><\/span>\n\tchild  Operator<\/span><\/span>\n\tgetter <\/span>func<\/span>(DBValue) T<\/span><\/span>\n}   <\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    \u518d\u6765\u770b\u770bfilter_op_test\u4e2d\u662f\u600e\u4e48\u521d\u59cb\u5316filter\u7684\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    _<\/span>, <\/span>t1<\/span>, <\/span>t2<\/span>, <\/span>hf<\/span>, <\/span>_<\/span>, <\/span>tid<\/span> := <\/span>makeTestVars<\/span>()<\/span><\/span>\n\thf.<\/span>insertTuple<\/span>(&t1, tid)<\/span><\/span>\n\thf.<\/span>insertTuple<\/span>(&t2, tid)<\/span><\/span>\n\t<\/span>var<\/span> <\/span>f<\/span> FieldType = FieldType{<\/span>"name"<\/span>, <\/span>""<\/span>, StringType}<\/span><\/span>\n\t<\/span>filt<\/span>, <\/span>err<\/span> := <\/span>NewStringFilter<\/span>(&ConstExpr{StringField{<\/span>"sam"<\/span>}, StringType}, OpEq, &FieldExpr{f}, hf)<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    func<\/span> <\/span>NewIntFilter<\/span>(constExpr Expr, op BoolOp, field Expr, child Operator) (*Filter[<\/span>int64<\/span>], <\/span>error<\/span>) {<\/span><\/span>\n\t<\/span>if<\/span> constExpr.<\/span>GetExprType<\/span>().Ftype != IntType || field.<\/span>GetExprType<\/span>().Ftype != IntType {<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>nil<\/span>, GoDBError{IncompatibleTypesError, <\/span>"cannot apply int filter to non int-types"<\/span>}<\/span><\/span>\n\t}<\/span><\/span>\n\t<\/span>f<\/span>, <\/span>err<\/span> := newFilter[<\/span>int64<\/span>](constExpr, op, field, child, intFilterGetter)<\/span><\/span>\n\t<\/span>return<\/span> f, err<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
     \u7ee7\u7eed\u6765\u76f4\u63a5\u770bToDo\u3002\u8fd4\u56de\u4e00\u4e2aDesc\uff1f\u4f46\u662fFilter\u91cc\u9762\u53ea\u6709child\uff0c\u4f5c\u4e3aheapfile\u6709Descriptor\u65b9\u6cd5\uff0c\u90a3\u76f4\u63a5\u8fd4\u56de\u5373\u53ef\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    \/\/ Return a TupleDescriptor for this filter op.<\/span><\/span>\nfunc<\/span> (f *Filter[T]) <\/span>Descriptor<\/span>() *TupleDesc {<\/span><\/span>\n\t<\/span>\/\/ TODO: some code goes here<\/span><\/span>\n\t<\/span>return<\/span> f.child.<\/span>Descriptor<\/span>()<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    \u81ea\u5df1\u5199\u4e2atest\u770b\u770b\u8f93\u51fa\u7ed3\u679c<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    func<\/span> <\/span>TestDescriptor<\/span>(t *testing.T) {<\/span><\/span>\n\t<\/span>_<\/span>, <\/span>t1<\/span>, <\/span>t2<\/span>, <\/span>hf<\/span>, <\/span>_<\/span>, <\/span>tid<\/span> := <\/span>makeTestVars<\/span>()<\/span><\/span>\n\thf.<\/span>insertTuple<\/span>(&t1, tid)<\/span><\/span>\n\thf.<\/span>insertTuple<\/span>(&t2, tid)<\/span><\/span>\n\t<\/span>var<\/span> <\/span>f<\/span> FieldType = FieldType{<\/span>"age"<\/span>, <\/span>""<\/span>, IntType}<\/span><\/span>\n\t<\/span>filt<\/span>, <\/span>err<\/span> := <\/span>NewIntFilter<\/span>(&ConstExpr{IntField{<\/span>25<\/span>}, IntType}, OpGt, &FieldExpr{f}, hf)<\/span><\/span>\n\t<\/span>if<\/span> err != <\/span>nil<\/span> {<\/span><\/span>\n\t\tt.<\/span>Errorf<\/span>(err.<\/span>Error<\/span>())<\/span><\/span>\n\t}<\/span><\/span>\n\t<\/span>desc<\/span> := filt.<\/span>Descriptor<\/span>()<\/span><\/span>\n\tfmt.<\/span>Printf<\/span>(<\/span>"filter desc: <\/span>%v<\/span>\\n<\/span>"<\/span>, desc)<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    \u55ef\uff0c\u6ca1\u6bdb\u75c5\u3002<\/p>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    <\/div>\n\n\n\n
    \n
    \u5b9e\u9a8c\u6b65\u9aa4<\/p>\nIterator<\/em><\/cite><\/blockquote>\n\n\n\n
    \u53c8\u8981\u5199\u4e2a\u8fed\u4ee3\u5668\uff0c\u90a3\u5148\u6765\u770b\u770b\u8981\u5b9e\u73b0\u4ec0\u4e48\u5427\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    \/\/ Filter operator implementation. This function should iterate over<\/span><\/span>\n\/\/ the results of the child iterator and return a tuple if it satisfies<\/span><\/span>\n\/\/ the predicate.<\/span><\/span>\n\/\/ HINT: you can use the evalPred function defined in types.go to compare two values<\/span><\/span>\nfunc<\/span> (f *Filter[T]) <\/span>Iterator<\/span>(tid TransactionID) (<\/span>func<\/span>() (*Tuple, <\/span>error<\/span>), <\/span>error<\/span>) {<\/span><\/span>\n\t<\/span>\/\/ TODO: some code goes here<\/span><\/span>\n\t<\/span><\/span>\n\t<\/span>return<\/span> <\/span>nil<\/span>, <\/span>nil<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
    \u6839\u636e\u4e4b\u524d\u5728heap file\u548cheap page\u4e2d\u7f16\u5199\u8fed\u4ee3\u5668\u7684\u7ecf\u9a8c\uff0c\u5148\u5199\u4e2a\u533f\u540d\u51fd\u6570\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    func<\/span> (f *Filter[T]) <\/span>Iterator<\/span>(tid TransactionID) (<\/span>func<\/span>() (*Tuple, <\/span>error<\/span>), <\/span>error<\/span>) {<\/span><\/span>\n\t<\/span>\/\/ TODO: some code goes here<\/span><\/span>\n\t<\/span>return<\/span> <\/span>func<\/span>() (*Tuple, <\/span>error<\/span>) {<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>nil<\/span>, <\/span>nil<\/span><\/span>\n\t}, <\/span>nil<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    \u63a5\u4e0b\u6765\u60f3\u4e0b\u8be5\u5b9e\u73b0\u4ec0\u4e48\u529f\u80fd\u3002Filter\uff0c\u5b57\u9762\u610f\u601d\u6765\u7406\u89e3\u7684\u8bdd\u5c31\u662f\u7b5b\u9009\u51fa\u7279\u5b9a\u7684\u5b57\u6bb5\u3002\u540c\u65f6\u6ce8\u91ca\u4e2d\u53c8\u63d0\u5230\u4e86\u904d\u5386\u5b50\u8fed\u4ee3\u5668\u7684\u6240\u6709\u7ed3\u679c\uff0c\u5e76\u8fd4\u56de\u5408\u9002\u7684tuple\u3002\u90a3\u5148\u5199\u4e2a\u5927\u81f4\u7ed3\u6784\u51fa\u6765\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    func<\/span> (f *Filter[T]) <\/span>Iterator<\/span>(tid TransactionID) (<\/span>func<\/span>() (*Tuple, <\/span>error<\/span>), <\/span>error<\/span>) {<\/span><\/span>\n\t<\/span>\/\/ TODO: some code goes here<\/span><\/span>\n\t<\/span>iter<\/span>, <\/span>err<\/span> := f.child.<\/span>Iterator<\/span>(tid)<\/span><\/span>\n\t<\/span>if<\/span> err != <\/span>nil<\/span> {<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>nil<\/span>, err<\/span><\/span>\n\t}<\/span><\/span>\n\t<\/span>return<\/span> <\/span>func<\/span>() (*Tuple, <\/span>error<\/span>) {<\/span><\/span>\n\t\t<\/span>for<\/span> {<\/span><\/span>\n\t\t\t<\/span>tuple<\/span>, <\/span>err<\/span> := <\/span>iter<\/span>()<\/span><\/span>\n\t\t\t<\/span>if<\/span> err != <\/span>nil<\/span> || tuple == <\/span>nil<\/span> {<\/span><\/span>\n\t\t\t\t<\/span>return<\/span> <\/span>nil<\/span>, err<\/span><\/span>\n\t\t\t}<\/span><\/span>\n\t\t\t<\/span>return<\/span> tuple, <\/span>nil<\/span><\/span>\n\t\t}<\/span><\/span>\n\t}, <\/span>nil<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
    test\u4e00\u4e0b\u770b\u770b\u80fd\u8f93\u51fa\u4ec0\u4e48\u3002<\/p>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    \u8fd4\u56de\u7684cnt\u662f2\uff0c\u800c\u6211\u4eec\u9700\u89811\uff0c\u8bf4\u660e\u7f3a\u5c11if\u5224\u65ad\u662f\u5426\u5339\u914d\u7684\u6761\u4ef6\u3002\u4f46\u662fif\u5230\u5e95\u5e94\u8be5\u5224\u65ad\u4ec0\u4e48\u5462\uff1f<\/p>\n\n\n\n
    \u522b\u5fd8\u4e86\u6211\u4eec\u8fd8\u6ca1\u7528\u4e0aFilter\u3002\u6211\u4eec\u6253\u4e2a\u65ad\u70b9\u770b\u770b\u6b64\u65f6filter\u4e2d\uff0c\u5404\u4e2a\u6570\u636e\u6210\u5458\u7684\u503c\u662f\u4ec0\u4e48\u3002<\/p>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    op\u7684\u503c\u662fopgt?\u60f3\u5230gt\u90a3\u5c31\u662fgreater than\u3002\u90a3\u4e48\u4e3a\u4ec0\u4e48\u8981\u63d0\u5230op\u5462\uff1f\u6ce8\u91ca\u4e2d\u63d0\u5230\u4e00\u70b9<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    \/\/ HINT: you can use the evalPred function defined in types.go to compare two values<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    \u90a3\u6211\u4eec\u5c31\u770b\u770bevalPred\u662f\u5e72\u4ec0\u4e48\u7684\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    func<\/span> evalPred[T constraints.Ordered](i1 T, i2 T, op BoolOp) <\/span>bool<\/span> {<\/span><\/span>\n\t<\/span>switch<\/span> op {<\/span><\/span>\n\t<\/span>case<\/span> OpEq:<\/span><\/span>\n\t\t<\/span>return<\/span> i1 == i2<\/span><\/span>\n\t<\/span>case<\/span> OpNeq:<\/span><\/span>\n\t\t<\/span>return<\/span> i1 != i2<\/span><\/span>\n\t<\/span>case<\/span> OpGt:<\/span><\/span>\n\t\t<\/span>return<\/span> i1 > i2<\/span><\/span>\n\t<\/span>case<\/span> OpGe:<\/span><\/span>\n\t\t<\/span>return<\/span> i1 >= i2<\/span><\/span>\n\t<\/span>case<\/span> OpLt:<\/span><\/span>\n\t\t<\/span>return<\/span> i1 < i2<\/span><\/span>\n\t<\/span>case<\/span> OpLe:<\/span><\/span>\n\t\t<\/span>return<\/span> i1 <= i2<\/span><\/span>\n\t<\/span>case<\/span> OpLike:<\/span><\/span>\n\t\t<\/span>s1<\/span>, <\/span>ok<\/span> := <\/span>any<\/span>(i1).(<\/span>string<\/span>)<\/span><\/span>\n\t\t<\/span>if<\/span> !ok {<\/span><\/span>\n\t\t\t<\/span>return<\/span> <\/span>false<\/span><\/span>\n\t\t}<\/span><\/span>\n\t\t<\/span>regex<\/span>, <\/span>ok<\/span> := <\/span>any<\/span>(i2).(<\/span>string<\/span>)<\/span><\/span>\n\t\t<\/span>if<\/span> !ok {<\/span><\/span>\n\t\t\t<\/span>return<\/span> <\/span>false<\/span><\/span>\n\t\t}<\/span><\/span>\n\t\t<\/span>regex<\/span> = <\/span>"^"<\/span> + regex + <\/span>"$"<\/span><\/span>\n\t\t<\/span>regex<\/span> = strings.<\/span>Replace<\/span>(regex, <\/span>"%"<\/span>, <\/span>".*?"<\/span>, -<\/span>1<\/span>)<\/span><\/span>\n\t\t<\/span>match<\/span>, <\/span>_<\/span> := regexp.<\/span>MatchString<\/span>(regex, s1)<\/span><\/span>\n\t\t<\/span>return<\/span> match<\/span><\/span>\n\t}<\/span><\/span>\n\t<\/span>return<\/span> <\/span>false<\/span><\/span>\n<\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
    \u8fd9\u4e0d\u5c31\u662f\u6839\u636e\u8f93\u5165\u7684op\uff0c\u518d\u8fdb\u884c\u76f8\u5e94\u7684\u6761\u4ef6\u5224\u65ad\u561b\u3002\u6bd4\u5982op\u662fopgt\uff0c\u5de6\u503c\u662fuser_id\uff0c\u53f3\u8fb9\u662f2\u7684\u8bdd\uff0c\u5199\u6210\u5bf9\u5e94\u7684SQL\u5c31\u5e94\u8be5\u662f<\/p>\n\n\n\n
    WHERE user_id opgt 2<\/em><\/strong><\/p>\n\n\n\n
    \u90a3\u5c31\u597d\u5199\u4e86\u3002\u53bb\u5bf9\u5e94\u5b57\u6bb5\u7684\u503c\uff0c\u7136\u540e\u6839\u636eop\u8fd4\u56detrue\u8fd8\u662ffalse\u6765\u7b5b\u9009\u6700\u540e\u5f97\u5230\u7684\u6570\u636e\u3002<\/p>\n\n\n\n
    Go<\/span><\/path><\/path><\/svg><\/span>
    func<\/span> (f *Filter[T]) <\/span>Iterator<\/span>(tid TransactionID) (<\/span>func<\/span>() (*Tuple, <\/span>error<\/span>), <\/span>error<\/span>) {<\/span><\/span>\n\t<\/span>\/\/ TODO: some code goes here<\/span><\/span>\n\t<\/span>iter<\/span>, <\/span>err<\/span> := f.child.<\/span>Iterator<\/span>(tid)<\/span><\/span>\n\t<\/span>if<\/span> err != <\/span>nil<\/span> {<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>nil<\/span>, err<\/span><\/span>\n\t}<\/span><\/span>\n\t<\/span>return<\/span> <\/span>func<\/span>() (*Tuple, <\/span>error<\/span>) {<\/span><\/span>\n\t\t<\/span>for<\/span> {<\/span><\/span>\n\t\t\t<\/span>tuple<\/span>, <\/span>err<\/span> := <\/span>iter<\/span>()<\/span><\/span>\n\t\t\t<\/span>if<\/span> err != <\/span>nil<\/span> || tuple == <\/span>nil<\/span> {<\/span><\/span>\n\t\t\t\t<\/span>return<\/span> <\/span>nil<\/span>, err<\/span><\/span>\n\t\t\t}<\/span><\/span>\n\t\t\t<\/span>leftVal<\/span>, <\/span>_<\/span> := f.left.<\/span>EvalExpr<\/span>(tuple)<\/span><\/span>\n\t\t\t<\/span>rightVal<\/span>, <\/span>_<\/span> := f.right.<\/span>EvalExpr<\/span>(tuple)<\/span><\/span>\n\t\t\t<\/span>tmp<\/span> := <\/span>evalPred<\/span>(f.<\/span>getter<\/span>(leftVal), f.<\/span>getter<\/span>(rightVal), f.op)<\/span><\/span>\n\t\t\t<\/span>_<\/span> = tmp<\/span><\/span>\n\t\t\t<\/span>if<\/span> <\/span>evalPred<\/span>(f.<\/span>getter<\/span>(leftVal), f.<\/span>getter<\/span>(rightVal), f.op) {<\/span><\/span>\n\t\t\t\t<\/span>return<\/span> tuple, <\/span>nil<\/span><\/span>\n\t\t\t}<\/span><\/span>\n\t\t}<\/span><\/span>\n\t}, <\/span>nil<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
    run\u4e00\u4e0btest\uff0c\u4e24\u4e2atest\u90fd\u80fd\u8fc7\u3002<\/p>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    \u4e0b\u7bc7\u518d\u770b\u770b\u600e\u4e48\u5b9e\u73b0join\uff0c\u4e89\u53d62\u5929\u5185\u5199\u5b8c\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
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