Swift Dictionary updateValue()

In this tutorial, we will learn about the Swift Dictionary updateValue() method with the help of examples.

The updateValue() method updates the value in the dictionary for the given key.


// create a dictionary with two elements
var information = ["Charlie": 54, "Harvey": 34]

// update value of "Charlie" to 57 information.updateValue(57, forKey: "Charlie")
// print updated dictionary print(information) // Output: ["Charlie": 57, "Harvey": 34]

updateValue() Syntax

The syntax of the updateValue() method is:

dictionary.updateValue(new_value, forKey: key)

Here, dictionary is an object of the Dictionary class.

updateValue() Parameters

The updateValue() method takes one parameter:

  • new_value - the new value to add
  • key - the key whose value is to be updated.

Note: If the key doesn't already exist, the new key-value pair is created.

updateValue() Return Value

  • The updateValue() method returns the value that was replaced.

Note: The method returns nil if new key-value pair is added.

Example 1: Swift updateValue()

// create a dictionary with two elements
var marks = ["Sabby": 78, "Nick": 59]

print("Marks Before:", marks)

// update value of "Nick" to 67 marks.updateValue(67, forKey: "Nick")
// print updated dictionary print("Marks After:", marks)


Marks Before: ["Nick": 59, "Sabby": 78]
Marks After: ["Nick": 67, "Sabby": 78]

Example 2: Create new key-value Pair

// create a dictionary with two elements
var marks = ["Sabby": 78, "Nick": 59]

print("Before:", marks)

// associate value 45 to new key Sazz marks.updateValue(45,forKey: "Sazz")
// print updated dictionary print("After:", marks)


Before: ["Sabby": 78, "Nick": 59]
After: ["Sabby": 78, "Nick": 59, "Sazz": 45]

Here, since there is no key named "Sazz" in the marks dictionary, so the new key-value pair is created.

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