Solidity Tutorial: All About Conditionals | by Jean Cvllr | Apr, 2022

picture by Alex Padurariu on Unsplash

Everybody writing code each day is aware of what a if / else assertion is. However nonetheless, since we’re within the “All About Solidity” article series, we’ll cowl all the pieces concerning the Solidity sensible contract language!

No bent guidelines! We can not omit conditionals!

In right this moment’s article, we are going to nonetheless cowl the fundamentals of conditionals in Solidity, and a few of their variants.

However as an alternative of re-explaining if statements over again from scratch, we are going to the Solidity code of 4 extremely popular sensible contract tasks: CryptoKitties, BarnBridge, Sablier, and LUKSO.

So we are able to as effectively be taught and perceive how some widespread sensible contracts work and enhance our curiosity.

OverviewInstance 1 — CryptoKitties
Fundamental if assertion (one situation)
Both one situation or one other with ||
Use a variable as a situation
Instance 2 — BarnBridge
Concatenating a number of situations with &&
if … else …
Instance 3 — Sablier
One line if statements
What else may be written inside if statements in Solidity?
Instance 4 — LUKSO
omitting curly braces
Remaining Notes on Solidity conditionalsReferences

Conditionals in Solidity observe the fundamental constructs of different programming languages:

  • a situation is wrapped contained in the brackets of an if assertion.
  • if the situation evaluates to true, the code contained in the curly brackets runs.
  • if the situation evaluates to false, this system execution jumps to the following assertion after the closing bracket }.

Nothing new right here! However let’s see in apply with some actual Solidity code at the moment operating on mainnet!

Fundamental if assertion (one situation)

if ( <condition-to-be-met> ) 
// run this Solidity code...

Kittens “can not breed with themselves”. So we can not present the identical ID for the matron and the sir. So if the matron is similar because the sir, it’s not a sound mating pair. See KittyBreeding.sol, line 134.

// A Kitty cannot breed with itself!        
if (_matronId == _sireId)
return false;

Both one situation or one other

Kitties can not breed with their dad and mom as anybody would possibly guess. So neither the male guardian (sire) nor the feminine guardian (matron).

This may be accomplished through the use of the short-circuiting operator || contained in the conditional. If not less than one of many two situations evaluates to true, the code contained in the if block will run.

Within the case of CryptoKitties, the maiting pair might be invalid. See the KittyBreeding.sol, line 139.

// Kitties cannot breed with their dad and mom.        
if (_matron.matronId == _sireId || _matron.sireId == _sireId)
return false;
if (_sire.matronId == _matronId || _sire.sireId == _matronId)
return false;

Use a variable as a situation

The primary widespread NFT recreation CryptoKitties makes use of an Public sale mechanism below the hood. It features a function known as autobirth, enabling anybody to arrange a daemon to name the giveBirth(...) operate on the proper time.

That is mainly the equal to:

Mining CryptoKitties ! ⛏ 😸 🙀 ⛓

The autobirth choice in cryptokitties may be discovered within the contract KittyAuction.sol. If the bid within the public sale contains the autobirth charge, the doAutoBirth mode will get activated and used to create the brand new cryptokitten. An extra AutoBirth occasion is emitted on the community, as a sign that the cryptokitten was created by a daemon.

if (doAutoBirth)             
// Auto delivery charge offered, set off autobirth occasion
Kitty storage matron = kitties[_matronId];
AutoBirth(_matronId, matron.cooldownEndTime);
picture supply:

We are going to take a look at extra types of conditionals in sensible contracts by wanting on the Solidity code of BarnBridge.

BarnBridge is a protocol that goals to wager on threat in Defi. Customers should buy bonds (within the type of tokens) and use these bonds to wager on potential dangers that different Defi protocols can encounter (e.g: inflation, variations in Defi rates of interest, costs volatility of the underlying ERC20 tokens of the Defi protocol, and so forth…).

They provide a number of merchandise/bonds specifics to totally different threat classes. Smart Yields is one among them, and focuses on variation in Defi rates of interest.

In Abstract, BarnBridges goals to:

Tokenize dangers within the Defi panorama

Let’s take a look at the SmartYield.sol contract, for extra examples of if conditionals.

Concatenating a number of situations

You may concatenate situations utilizing the short-circuiting operator && .

In BarnBridge, that is used to verify for expired bonds. An unliquidated senior bond needs to be eliminated as quickly because it has reached maturity. See line 576 in SmartYield.sol

If … Else …

The traditional if assertion doesn’t go unexplained with out the else assertion. Here’s a primary reminder:

  • if the situation evaluates to true, the code contained in the if block will run.
  • if the situation evaluates to false, the code contained in the else blcok will run.

Here’s a if ... else ... assertion from BarnBridge. It’s used to deal with a junior bond relying on its maturity date. See SmartYield.sol, line 326.

One line if statements

It’s doable to write down the code that needs to be run if the situation evaluates to true in the identical line of the if assertion (as an alternative of contained in theif block).

Right here is an ideal instance from the Sablier protocol. Take a better take a look at the function withdrawFromStream(...), particularly line 258.

If a consumer withdraws cash from a streaming “channel” he/she beforehand opened, the protocol checks for the remaining stability within the channel. If no funds are left, the channel is closed and deleted.

That is completed as a if assertion with a single line, with out opening a block with curly brackets.

What may be written inside if statements in Solidity?

Just about something! Based mostly on the logic of the contract. However some widespread examples are:

  • make exterior contract calls
  • return the operate

Listed below are two primary examples once more from Sablier.

The final function cancelStream(...) within the contract allows to cancel a stream, and can switch all of the tokens again to the supposed recipient of the stream.

You may see contained in the operate an exterior name (by way of token.safeTransfer(...) ) to the token contract that was used to pay for the stream. See Sablier.sol, strains 287–288.

As one other instance, the deltaOf(...) function contains two if statements that return instantly relying on the worth of the block.timestamp. See Sablier.sol, strains 101–102.

I’ve given two primary examples right here, however as you’ll be able to think about, if conditionals can result in just about something out there in Solidity. Different situations may very well be updating the contract state, or reverting.

LUKSO is a brand new EVM-based Blockchain centered on the brand new inventive economic system. It focuses extra on social and inventive use instances, relatively than Finance (Defi) or technical functions that at the moment pre-dominate the blockchain area.

LUKSO is user-centered, and may be described as a “Blockchain for the peoples”. It’s an ecosystem that can be utilized as the bottom for constructing functions extra related to “the on a regular basis consumer”. Such functions embody Common Profiles, cultural currencies, popularity techniques or relay companies.

We are going to deal with Common Profile right here 🆙. Common Profiles are sensible contract-based accounts that act as a profile id on the blockchain.

my Common Profile on

Need additionally to create your individual Common Profile? 🆙 Go to!

Such profiles are managed by a contract known as a KeyManager. The KeyManager supplies fine-grain management over your Common Profile, permitting you to grant particular permissions to different events or brokers (like Dapps, addresses that you just belief, or units that you just use to check in to your Common Profile).

Let’s take a look at a last variant instance of if statements from the LSP6KeyManagerCore.sol.

See additionally@lukso/lsp-smart-contracts on Github for the total Solidity code.

You can too learn Felix Hildebrandt’s 3 articles series for a great overview of the LUKSO ecosystem 🔎

Omitting curly brackets

In a if assertion in Solidity, if the situation being evaluated results in a one-line assertion, it’s doable to write down this assertion within the subsequent line and omit the curly braces of the if block. (please re-write this, it’s unimaginable to learn and perceive)

NB: Right indentation is required on this case.

The totally different permissions outline within the KeyManager provides the beneficiary the flexibility to carry out particular functionalities on behalf of the Common Profile. Such functionalities embody:

  1. enhancing the profile information.
  2. interacting with different contracts on the community.
  3. give possession of the Common Profile to a different handle.

Let’s take a look at 3). With a purpose to give possession of the Common Profile to a different handle (a brand new KeyManager, or a easy Externally Owned Account), the handle making the request should have a selected permission: CHANGEOWNER.

You’ll find this conditional if assertion line 268–269 of LSP6KeymanagerCore.sol. I’ve created a simplified gist for simplicity to go to the important.

Two last notes on conditionals in Solidity:

  • parentheses can’t be omitted for if conditionals.
  • Not like in C, there isn’t any sort conversion from non-boolean to boolean varieties.

Because of this the next assertion shouldn’t be legitimate in Solidity:

if (1) 
// ...

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