Why do I get a TypeError: no implicit conversion of symbol into Integer?

Question

I am playing around with nested hashes. Task:

Create three hashes called person1, person2, and person3, with first and last names under the keys :first and :last. Then create a params hash so that params[:father] is person1, params[:mother] is person2, and params[:child] is person3. Verify that, for example, params[:father][:first] has the right value.

My solution:

person1 = {first: "first_name1", last: "last_name1"}
person2 = {first: "first_name2", last: "last_name2"}
person3 = {first: "first_name3", last: "last_name3"}
params = { :father => ":person1", :mother => ":person2", :child => ":person3" }

then params[:father][:first] gives

TypeError: no implicit conversion of symbol into Integer

Why? I don't understand why I get the TypeError.

parameter access key value pair params = { :father => "person1", :mother => ":person2", :child => "person3" } and access params[:father] give result "person1" — Chaudhary Prakash
That is understood. It was passing more than one argument I was confused about. — Coder_Sav

Nic Nilov Nic Nilov · Accepted Answer · 2016-08-05T11:13:23

When you assign values to the params hash keys, you supply strings instead of personx hashes. The proper way would be instead of

params = { :father => ":person1"...

do

params = { :father => person1...

The reason for the error is as follows. This line:

params[:father][:first]

fetches the value of params[:father] first. You expect this value to be a hash, but due to the syntax error above it is a string. String does implement [] method just like hash but its semantics is different. It accesses a character within a string by its integer index. It expects the index to be passed as an argument to [].

Since you pass a symbol instead, [:first], and there is no default way to convert a symbol to integer, you get the appropriate error:

TypeError: no implicit conversion of symbol into Integer

Why do I get a TypeError: no implicit conversion of symbol into Integer?

3 Answers