Recommended Free Tools
To read a mapping owned by another deployed Solidity contract, call that contract’s public getter through a typed contract reference or interface, passing the mapping key. You cannot index another contract’s mapping as if its storage were yours. If a factory tracks multiple child contracts, first select the child, then pass the separate key for the child’s mapping.
Call the other contract’s getter, not its storage
Solidity generates a getter function for a state variable declared public. Another contract can call that function when it has a reference to the deployed contract. For example, if a contract declares mapping(address => uint256) public balances, a caller reads an account’s value with a.balances(account). The caller is invoking a function on a; it is not directly accessing a’s storage. See the Solidity contracts documentation.
A minimal interface lets the caller describe the getter it needs without importing the target contract’s full implementation:
interface IBalanceBook {
function balances(address account) external view returns (uint256);
}
contract Reader {
function readBalance(address book, address account)
external
view
returns (uint256)
{
return IBalanceBook(book).balances(account);
}
}The address supplied as book must be the deployed contract that implements the matching getter. The interface signature must match the target function’s inputs and outputs.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
Keep the factory index and mapping key separate
A factory may track several deployed child contracts, each of which has its own mapping. Reading an entry then takes two lookups: choose the child contract from the factory’s list, and pass that child’s mapping key to its getter. The IDs can share a Solidity type while representing different things.
In the example from Reading a Mapping That Lives on a Different Contract, the factory’s getter is:
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
function SfGet(uint256 _SimpleStorageDataID, uint256 _ID)
public view returns (string memory, address)
{
return ListOfSimpleStorageContracts[_SimpleStorageDataID].DataIdToData(_ID);
}_SimpleStorageDataIDselects a deployedSimpleStorageinstance from the factory’s list._IDis passed to that instance’sDataIdToDatapublic mapping getter to select an entry.- The return tuple contains the string and the owner address. Keep both if later logic needs the address for an ownership or authorization decision.
Mixing up the two IDs can call the right getter on the wrong child, or request the wrong entry from the selected child. Both arguments may be valid while identifying unintended data.
Reading mappings of structs
For a public mapping whose values are structs, Solidity’s generated getter returns the struct’s accessible members as outputs. A caller should declare and consume the returned tuple in the documented field order; it does not receive a storage reference to a struct held by another contract. Check the mapping declaration and getter signature rather than assuming every struct field is returned. The Ethereum Stack Exchange discussion of calling a mapping of structs covers this distinction.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
When a public getter is not enough
If the mapping is not public, another contract cannot call a compiler-generated mapping getter. The owning contract can instead expose a purpose-built external or public view function that returns the specific value or fields the caller needs. This is often useful for shaping a stable interface or avoiding exposure of unnecessary fields.
Reading is separate from writing. A getter returns data; it does not grant permission to modify the mapping. To change the target contract’s state, that contract must implement a state-changing function, and the function must enforce the intended authorization rules. An interface can declare that function for a caller, but cannot create write access by itself. The OpenZeppelin Forum discussion illustrates both the interface-based read and this write boundary.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
Know the key, or build an index
Mappings do not keep a list of their keys and have no built-in length or enumeration mechanism. If a caller needs to display or process every entry, the contract must maintain a separate key list or another index as entries are added. Otherwise, the reader needs to already know the key it wants to query. See Solidity’s documentation on mapping types.
A mapping behaves as though every possible key has a value initialized to the value type’s default. For example, an unset uint256 entry reads as zero. A default-valued result by itself therefore does not prove that the entry was explicitly written; track existence separately if that distinction matters.
The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Quick Recap
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
