github.com/dolthub/go-mysql-server@v0.18.0/sql/expression/function/function.go (about)

     1  // Copyright 2020-2021 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package function
    16  
    17  import (
    18  	"fmt"
    19  	"strings"
    20  
    21  	"github.com/dolthub/go-mysql-server/sql"
    22  	"github.com/dolthub/go-mysql-server/sql/expression"
    23  )
    24  
    25  type UnaryFunc struct {
    26  	expression.UnaryExpression
    27  	// Name is the name of the function
    28  	Name string
    29  	// The type returned by the function
    30  	RetType sql.Type
    31  }
    32  
    33  func NewUnaryFunc(arg sql.Expression, name string, returnType sql.Type) *UnaryFunc {
    34  	return &UnaryFunc{
    35  		UnaryExpression: expression.UnaryExpression{Child: arg},
    36  		Name:            name,
    37  		RetType:         returnType,
    38  	}
    39  }
    40  
    41  // FunctionName implements sql.FunctionExpression
    42  func (uf *UnaryFunc) FunctionName() string {
    43  	return strings.ToLower(uf.Name)
    44  }
    45  
    46  // EvalChild is a convenience function for safely evaluating a child expression
    47  func (uf *UnaryFunc) EvalChild(ctx *sql.Context, row sql.Row) (interface{}, error) {
    48  	if uf.Child == nil {
    49  		return nil, nil
    50  	}
    51  
    52  	return uf.Child.Eval(ctx, row)
    53  }
    54  
    55  // String implements the fmt.Stringer interface.
    56  func (uf *UnaryFunc) String() string {
    57  	return fmt.Sprintf("%s(%s)", uf.FunctionName(), uf.Child.String())
    58  }
    59  
    60  // Type implements the Expression interface.
    61  func (uf *UnaryFunc) Type() sql.Type {
    62  	return uf.RetType
    63  }